The 5.3 wiring harness will work fine on your 6.0 motor. The PCMs from 99-02 are the same hardware with different operating systems and calibrations on them. Get a PCM from an 02 model year truck (4.8, 5.3, or 6.0 engine) to be safe. Then you can have a programmer flash the correct operating system for your application (engine size, year, and transmission) plus do any customizations (VATS delete) that you may need.

What I'm in the process of right now is modifying an 88-92 TPI AC compressor bracket to work on my 6.0L so I can use my stock 95 AC compressor in the stock location. You have to ditch the EGR valve and get the car water pump so the water outlet doesn't come out the top. I haven't finished the supporting bracketry yet, but hopefully it will work out well in the end. You have to use the existing tensioner as an idler pulley and use the TPI tensioner as the "real" tensioner in this setup. Its kind of a wierd setup and I would much rather have the LS1 compressor and custom lines, but that would require some major work on my 4WD truck.

I made my own motor mounts out of 1/4" hot rolled steel.

I'm not completely sure of the differences between the LS1 style and SBC style transmission mount, but it seems you need a transmission designed for the new style engine. Grab an F-body trans from a wreck.

Oh on the gauges, be aware that most of the idiot lights on the cluster are operated by messages on the class 2 data bus generated by different modules on the network. I'm pretty sure the brake warning light is illuminated in this manner by the brake control module, as is the seat belt light, etc. Something to look out for.

Any more questions, I am almost done my swap and several others on this site have done similiar projects. I am hoping for a nice truck in a week or so!