I'll vote 350. Boring, bland and typical, but it will always work when you need it so long as you don't get too stupid. Plus, if this is your first project, it will give you a factory template to work off of instead of trying to engineer it all by yourself. Build something exotic later, for now just concentrate on building something that works. That is difficult enough for most first timers. Over reaching is probably the number one reason that so many project cars never see completion. It is easy to get burned out if you get in to far over your head. Read my build thread if you want to see just how complicated it can get using factory parts-and I know what I am doing.
For the wiring, just pull a complete engine bay harness out of a Chevy V8 engined G body from 1981 and you will be all set. While you are there, grab all the brackets, bolts and pulleys off the same car, and try to keep them together (use tape or sandwich bags, and keep stuff marked!). Take some good cell phone pics before and during the disassembly process. For a complete parts list, read the V6 to V8 swap stickies in the engine swap forum. Just remember that once you have managed to put it together once, you can take it apart at a later time to make it pretty. Most show cars are put together at least twice: Once to mock it up, do fabrication and be sure everything fits, and the next time after the fabrication is complete and everything is detailed. Also, go on E-Bay and buy a complete factory service manual set for your truck..err...car. It is an invaluable source of information when you are trying to put a car together from scratch. Expect to pay between $20 and $100 for the complete 3 book set, but trust me it's worth it.
You may also want to post where you live. That way, it will be easier to network with other board members if they are close to you and know of a good deal on something you need. Plus, they may be willing to help you out if you are willing to return the favor.