You can do the wiring with the stock harness, you'll just need the V8 part of the wiring. This can vary depending on what distributor you run, as well as whether you run an alternator or generator. If you're going to add aftermarket accessories, like a stereo, AC, etc., you might consider a Painless kit, but otherwise, the stock harness will be just fine.
Since you're considering a late 350 and automatic trans, you will not be eable to run the factory style V8 motor mounts. You'll need to use a side mount style or crossmember style. I would use the side mount style myself, cleaner installation. Those are available from Speedway, and mount to the tops of the framerails much like the later style engines mount.
For a carb, definetly go with a 4bbl. It's actually a myth that a 2bbl will get you better mileage, especially on a mid size V8 like a 350. Use a spreadbore carb with a progressive linkage, like a Q-Jet, or even a spreadbore Holley or Carter Thermoquad.
