[skyphix]

Engine mounts
Modified Harness (modify it yourself, send it out, or pick up a pre-made one... your choice)
the PCM will need to be flashed to get rid of anti-theft and a couple of O2 sensors
Your exhaust manifolds, I believe, will fit between the frame rails so you're good to go there (vs. truck ones, which don't fit without trimming)
Grab some of the exhaust - specifically the Y pipe so you can customize it to your needs
As others have said, the gas pedal, TAC module, and all associated wiring
There's someone here on the forum that makes an adapter bracket to bolt the DBW pedal in to your truck
Your driveshaft will have to be modified or replaced, most likely
Yes - a 2WD trans or convert your 4WD 4L60E to 2WD
You may have to make some modifications to your in-cab fuel tank - not sure exactly what people are doing with the 67-72's. On my 80 I am replacing the entire fuel system with a tank and sender from an FI Squarebody, using the pump from a later model Silverado, a corvette fuel regulator/filter, and either braided or nylon quick connect lines (haven't committed yet)
A speedometer can be tricky - I work in IT so I'm doing an OBDII driven digital dash (cheap android tablet and an app, plus customization to make it do what I want)