Re: engine oil, I agree w/ Aurora -- use 30-weight, but make sure that it's non-detergent. If you use a modern (read: detergent) oil, it'll break loose decades of accumulated goo that will gum up your bearings and cause all kinds of trouble you don't need.
If you feel comfortable dropping the lower crankcase and cleaning out all the tar and carbon in it with solvent, that would be great. As Aurora suggested, this would be a good time to see if some shims need to be removed to tighten things up...
There is no oil filter, and no oil pump; lower engine lubrication is accomplished by the "splash" system -- there are small "fingers" cast into the connecting rod caps that dip into the crankcase oil at the bottom of each stroke and fling oil onto the cylinder walls. Primitive, but it works -- and saved Henry Ford a couple of bucks on the production cost of each tractor.
The rear end and transmission do share the same lube, which is 600-weight (yes, six hundred!), also known as steam cylinder oil. Your Model F is equipped with a multi-disc *wet* clutch which requires this unusual lube for optimal performance. Don't use standard gear lube, as it contains sulfur which attacks the clutch's bronze discs (and other bronze components in the transmission/rear end).
While you're at it, it wouldn't be a bad idea to pull all of the grease cups, scrape the old, hard grease out, rinse them in solvent and refill with new wheel bearing grease (I use the red kind that comes in a 5-pound tub). Check the front wheel bearings; if you have time, scrape, rinse and repack them.
Pull the plugs and replace, or at least scrape the carbon off them. If you're going to replace them, the Autolite 3095 or Motocraft F-11 will work. Later on, if you want fancy show plugs, you can splurge and buy some of the repro "X"/Model T plugs that Champion still manufactures (dig deep, though; a set of four will cost between $80-100). Double-check the wires and make sure all ends give good contact.
Drain and clean out the sediment bulb, fuel tank and lines as best you can; there's probably a lot of rust, and eventually this rust will clog your sediment bulb and starve your engine for fuel.
Give the cooling system a good rinse; there's bound to be a lot of rust flakes. If it was my tractor, I'd just run water in it for a while until most of the loose flakes have rattled off. But make sure to drain the system this time of year to prevent freeze-ups. (The weak point is behind the coil box -- you'll frequently see these tractors or their engine blocks with broken castings or repairs in that spot. Don't let yours be another one...)
As for a manual, look on eBay; they are listed all the time (there were nearly 3/4 of a million of these tractors made, and a lot of manuals still survive, so don't believe anyone who gives you the "hard sell" and tries to convince you that their manual is a rare publication).
Hope the above notes help. Come on back with any other questions that may come up; somebody here is bound to know the answer, or can at least point you in the right direction.
Good luck, and let us know how you make out...
-- Maine Fordson