40 years ago I bought a Singer, but now a part is broken that can't be fixed nor replaced, unless I buy another old Singer. The pot-metal part isn't made anymore

My DL stopped and helped a couple with a flat tire, who were on their way to a flea market to sell some stuff. For his trouble, they gave him a White sewing machine, Model 1599 Jeans Machine - without a manual. I'm sure I will be able to figure out the tension adjustments, where to oil it, etc. since it's guts look similar to a Singer, but I need help figuring out how to thread it. It has what looks like a bobbin rewind on the top - is that where the spool of thread goes too? There's also small knobs on the top that thread could fit on, perhaps on a bobbin, but not big enough for a large spool. I noticed there were notches for the thread to travel through on the top, but the take-up lever is enclosed in the machine, although the left vertical side swings open. There's a horizontal structure that looks like a spool pin inside the left vertical, swing-out side; is that where the thread goes and it threads from left to right instead of right to left?There's also a slit in the left front machine body, that has a hook on it, that's totally enclosed. The thread doesn't seem to go through a tension regulator like my old Singer either. If I could figure out how to get it threaded that far, I think I could figure out how to thread it the rest of the way, maybe. Then I can figure out the tension, oiling, etc., maybe also. Help. I hope this old dawg isn't too old to learn a new trick.