Another V6 to 5.3 wiring question

[oneBADDz]

I'll be working on a 98 chevy vortec 4.3 truck. I have a 5.3 (cable TB)/tranny/harness/pcm.

Converting the harness to be standalone is fairly simple, is this the first step in wiring up this swap myself? If so, what do I have to do to make the guages etc on the truck end of the wiring work once the engine runs standalone? It seems to be the most simple method of getting this done, and I can do the standalone wiring, but I don't know what to do after that.
Buying a harness isn't out of the question, but I prefer to learn these things and not rely on outside sources if I don't have to.

It looks to me like most companies that make you a wire harness basically send you a standalone harness, but it is modified to use the old V6 computer to control non engine/tranny functions. I'd like to know how to make the standalone harness do the same thing if that's the best way to go about it. I'd also like to know which computer controls the guages, cruise control, etc.