I dont know where you are from, what kind of emissions/inspection laws you have to deal with, but putting those aside for a little while, I think your best bang for the buck would be a small block 400. Big cubes, small package.. Next on the list, if money is an issue, is a good old 350.. there is just SO much you can do.. I could talk for hours and hours about mods, performance parts, etc.. but I wont
I think you should seriously consider a nice (9.5:1, aftermarket aluminum heads, headers, free flowing exhaust) 350 with an aftermarket fuel injection (multi-port!) system.. that would give you unbeatable performance with the best economy.. even with an RV cam I bet you could push 300hp easy from that setup.. just a thought... it all depends on what you wanna do, and how much you wanna spend to do it..