[Clyde65]

1. Either one, but the pedal would be easier to mount for a DBW IMO.
2. I would go with a boyd tank ( vendor here) his tank will run around 700.
3. I used CSLS1 Sanderson shorties, they are reasonably priced and work great, TBSS manifolds would be the best manifold option.
4. I would buy a harness from PSI (psiconversion.com) or one like that

I put a 2005 4.8/4l60e in my 65, plenty of power, I also swapped the DBW to a DBC, the only thing I need to work on is my cruise and pretty-ing up the accelerator.

If you do the DBC just get the cruise module from a truck. also you can get with LS1nova ( I think) he can convert a early 80's van cruise switch to work on your column.

Also make sure you check out the LS swap thread here, more information than you can digest.