Dyantech pretty much summed it up on the wiring. I did my own harness cutting and splicing and if I would of had the money I would have definitely went with a custom harness like dynatch will make for you. It will save a lot of time, and now days, my time is very limited, lol.

The trans should mount up just fine to the crossmember.
You need about 60psi for the ls1 to run properly. Get a gauge from summit and attach it to the shrader valve.
You should be able to get some mounts from a v8 truck to make it work. The truck and ls1 engines have the same mounting bosses.

Good luck posting this on other forums and having this kind of info lol, all you'll get is "why swap out a v6, just get a v8 truck"

I say got for it, and keep us updated, there's enough ppl here to get your thru it.

allen