Do you have the MTD belt number handy and are your sure it's a MTD some in the early 80's were still made by Gilson. If you have the belt number you can use the MTD detailed parts finder in this link it on the upper right hand side of the page. One there enter your Belt number if it a MTD it will show where the belt is used and will probaly give your a diagram of how its routed.

Here is a link that might be useful: MTD parts Catalog

I have an '87 Monkey Wards MTD (12HP, 38"deck) but it has the variable speed pulley system with front and rear drive belts so probably won't do you much good. Too bad because I have the manual and all the steps involved.

Hello Sergeant, It's made by MTD. I went to the MTD parts catalog, but it was no help.
I pull a 36" tine areator behind the tractor, and its loaded with a 100 lbs of weight. The original drive belt would only last a year under heavy torque loads, its a 4l820 belt. So, I now run a 5l820 belt which can last up to 3 or 4 years. The additional width on the belt agrees with the pulleys giving better gripping power.
All I really need is an Exploded Picture view showing the belts INSTALLED. From there, I can probally figure things out. Please, advise on this additional information. Thanks, Nitro.

THIS IS A FOLLOW-UP ...... The drive belt "letter" within the number may be misleading ..... Rather than 5l820, I should have listed it as ... 5 Larry 820 . I hope this clears-up any confusion ! Thanks, Nitro.

The first one i did, and i had never done an MTD type of belt replacement, turned out to be easier than first thought!
I found, the deck belt can be removed from the engine pulley, and tied out of the way. Then depress the brake/clutch pedal all the way down, and clamp it down! This releases tension on the belt. From there, you must look for any other things that may impede removal and replacement, and from there on, it is self-explanatory, more or less. I had the tractor setting on four jack-stands, so it was much easier to work on.
Some manufacturers do invent tricky things that do get in the way of belt replacement, but with a careful look-see, it will eventually show the path to replacement. Of course, you can always take it to a repair shop, a statement that makes do-it-yourselfers cringe, but if thats the only way out--do it!