you can use any gen 1 block so anything up to 98 with some exceptions, theres large debates between 2 bolt and 4 bolt for a mild build 2 bolt will hold up fine, resarch the block you have, i higher nickel content is ideal as itll have less cylinder wear but with any engine youll want the block checked out throughly for cracks, rebored, main aligned and all that to do it properly, if the cam you pick is roller your looking for an 88(in most cases) and up block.
its good to get an idea of what parts youd like to use but i always get my block checked out before so i know if i have to order large bearings rings and pistons.
after thats all set and done pick your parts and have your rotating assembly balanced.
i would greatly urge against porting the stock heads and intake, yes ive done it and truthfully its really not worth it at all. you can shop around cragislist and ebay all day for a good carb-tbi or carb-vortec or just carb intake for dirt cheap.
as for heads a decent set of lightly touched 083's, vortecs(need to take to machine shop to check for cracks, which is why i personally dont like them) or something along those lines will do much better. you can get some lower end pep out of tbi heads but youll always run out of room at 4500rpm due to the design of the head.
Like saatr said, the older the block you have youll gain mechincal pump provisions thatll need to be blocked out if not used, youll lose roller cam readyness unless you buy an expensive retrofit kit, and youll also have a 2 piece rear main as oppsoed to a 1 piece, which theres as much debate about that as there is 2 bolt mains vs 4 bolt vs splayed mains etc etc etc.
