questions about my new 65 mustang

[bmxmon]

Hey, I have quite a few questions I need some help with. I just bought a early 1965 mustang, with generator and all. So one of my questions is, will i be albe to swith over to a alternator with no problems? It has a 250 inline 6 in it right now, (not the original engine, is supposed to be a 170 ci) with a 3 speed manual tranny. If I get a 302 or 289, what do I need to change? Im pretty sure that I will need new front springs, but was wondering if the tranny will still work with a 302. Also, is there anything in the rear end that I will need to change out? I believe it has 3.1:1 gears in the rear end. Im 17, and pretty new to all this automotive stuff. I have read alot about it all, but never really actually done much. The 250 engine in there now runs really rough, and my brother in law said I need new head gaskets and exhaust manifold gaskets. The 250 is burning and leaking alot of oil, so I was thinking about just trying to get a new engine in there, because i was going to anywho. Also, he said that the piston rings might be bad. Thats all i can think of, thanks for looking, and helping if you can.