81 YZ100H Questions

I'd picked up a tired old 1981 YZ100. I've just finished
a complete restoration of the frame, wheels front and rear suspensions. The
plastic is not broken, but is badly faded and scratched... All of it!
I've just opened up the motor for the first time, and the
piston and cylinder are statndard size... Strangely, the
rest of the motor appears shot,while the trans and clutch are still good.
I am hoping someone can clue me in on the cheapest way
to acquire a crank and rod assembly for this thing. And the fuel tank, side
cover and fenders too. I don't believe it is worth my throwing a ton of
money at, but I'd like for it to look and run as well as reasonable.
I've not had a bike in almost 30 years... LOL
My last bike was a 1971 Hodaka Super Rat. I'm looking
to get out with my son when we pick up his new TTR100 next week. And would
like this YZ to cart this old man around when my boy goes out.

Thanks