I am curious what parts you are calling "crankshaft supports". (link to IPL below)
I don't read anything in your post about valve adjustment. Have you adjusted the valves?
"All keys are in good shape" How much torque did you use to tighten the flywheel retention nut? That nut needs 100 ft lb of torque to hold the flywheel securely to the crankshaft. If not torqued properly, the flywheel can shear the key enough when the starter cranks the engine to throw the spark timing off enough to cause what you are experiencing.
There is also a right way and a few wrong ways to install the flywheel key. Only the right way can assure the flywheel will seat squarely on the crankshaft taper. The right way is to set the flywheel onto the crank with the mating keyways aligned. Then very carefully insert the key into the slot and lightly tap it down flush. Then put the washer and nut on the crankshaft and torque the nut to spec torque. Do not use any oil or other lube on the crankshaft taper or the flywheel taper. If you did not do any of the above (valve adjust and flywheel install), you have some things to recheck. There is also a specific way to set the engine to adjust the valves.

Here is a link that might be useful: 31P777 IPL

Counterweight link is the parts that we're crushed when the old valve sheared sorry I should've referenced the ipl. I'm not sure its torqued to 100 but I pulled the flywheel again yesterday and the key is intact and that is the method I used to install the key, I'll probably do it again though just to be sure, how much deformation does it take before there are negative results? I read the valve adjustment post but didn't really understand how to do it is there another link that would be useful?
I'm also at a loss on this carb, I believe I reassembled it correctly but I don't have an original diagram that shows it together. Currently rod and spring from governor are attached to throttle butterfly and choke butterfly is attached to a short piece of looped metal so it just floats open until the throttle is fully on then it engages. I'm used to motorcycle carbs that have a lot more control I'm probably just overthinking this but wanted to be sure.
Theres a small dent in the top of the piston from the old valve as well, I haven't tested compression yet (I can definately hear and feel its presence) do you know what value I should have?

I have DETAILED instructions for adjusting your valve IF you would like them. Address below, put in proper format.

I was sure wondering also what crankshaft supports were.

Walt Conner
wconner5 at verizon dot net

Yeah I couldn't think of what to reference them as and thats the closest I could come up with. I appreciate both of your assistance hopefully tomorrow I can make something happen with this engine.

Does anyone know where I can download a shop manual for this engine?

Walt I was just wondering if you got my email?

"Walt I was just wondering if you got my email?"

NO, you did put .net NOT .com?

Walt Conner
wconner5 at verizon dot net

Are there any other components to the compression release? Whenever I put the valves to spec it takes a lot to spin the flywheel seeming to stall it out.

Are you properly confirming the cylinder is actually at TDC of the COMPRESSION stroke, and then turning the crank a bit further in the correct direction of engine rotation until the piston moves down just 1/4" before setting both valves? If you are not confirming all this to be true, you may not be accomplishing a genuine, accurate, Briggs valve adjustment.

My Instructions include a test for compression release.

Walt Conner

It seems to be in the right spot, 1/4" past top end of the stroke. I'm close I think, it'll run for a bit but is occasionally backfiring out of the carb. I'm feathering the valve tension back and forth a bit is there anything else to fine tune to clear up running?

Oh note on lessons learned, the key to the flywheel is shaped I had it in backwards so there was some slack there too.

***"the key to the flywheel is SHAPED I had it in backwards"***
The key is not "shaped". The key is supposed to be straight, and there should be no appreciable "slack" in the fit.
If the key appears to be shaped (as I understand your description) it means that the flywheel has shifted out of place and partially sheared the key. This key needs to be replaced with a genuine Briggs part. Refer to my other post above regarding the key. You need a torque wrench to be sure the flywheel is being tightened firmly enough.
What exactly do you mean by "feathering the valve tension back and forth a bit"?????
Another thing, I hope you understand that "1/4" past top end of stroke" does not confirm that you are actually using the top end of the COMPRESSION stroke. There are 2 times in the 4 stroke cycle that the piston is at Top Dead Center (TDC). 1 time is at the end of the COMPRESSION stroke, the other time is at the end of the EXHAUST stroke.
I can believe you are probably in the right position but unless you know you are there by understanding the difference..........then there is room for doubt.

I'll have to apologize again reading back my descriptions are really lacking in my posts. The key is rectangular, when you mentioned it would need to be tapped in I pulled it and saw that it wasn't as tight as i thought, but once spun 90* it fits like a glove and seats everything nicely.
With the valve tension, I'm judging TDC based on when the intake valve closes, Walts instructions are great, I'm not seeing the second release of the intake valve to indicate compression release and I am having issues with too compression being too great to restart when it stalls. I am new to adjusting valves so I could very likely be doing it incorrectly, I'm using a new well lubed feeler gauge, .003-.005 (intake) and .005-.007 (exhaust) for the gap. I'm setting it so that its almost grinding to slide it through but not quite, then I hold the nut with a wrench while setting the lock screw. At this point it'll run for a bit but if I shut it off compression locks up the cylinder (I'm cranking it with a marine battery now just to ensure power isn't an issue). I can get it to turn over if I try a couple times but then it'll backfire through the carb from time to time. Your help so far has been invaluable I've gone from an engine that wouldn't do anything to something close to servicable. I'm just trying to work out the bugs so I can get her back out of my garage and put to work. Thanks again.

"Grinding", that might be a bit tight (by my definition of "grindingly tight"). There really should not be any "tension" on the feeler gauge at all. What we are trying to establish is the proper amount of CLEARANCE or empty space between the end of the valve and the rocker arm. You really want the feeler gauge blade to slide very easily when it is withdrawn from the rocker/valve juncture, and it should slide back into the same without your having to force it or manually push the valve open to get it back into the space. Or in other words, you want the open space to be exactly the same amount as the thickness of the feeler gauge blade. If you can actually feel the drag or resistance against the blade, you are too tight (too little gap).
Do this: Turn the engine while watching the valve action. When you turn the engine so that the intake valve has been pushed down as far as it will go, measure the height of the valve spring from the cylinder head up to the top of the valve spring washer (use a small pocket ruler). Carefully read the dimension and record the value. Next, turn the engine until you see the exhaust valve move down as far as it will go. Measure the same way as before and compare the 2 values. The distance should be identical (or within 1/32" inch) for both valves. If you measure a difference of 1/8" or so between the 2 values, the camshaft is worn out (a possibility on 31 series engines).