[Gmecm] ECU / PROM questions

[Sam Reed]

Does it matter if a P4 PROM was originally for a speed density or MAF 
system when customizing?  Does the ECU care about SD v. MAF?  Is there 
anything about displacement hard-wired into the limp-home mode chips 
(i.e. as long as you have the right number of cylinders, are you ok)?

I need to find a V8 P4 chip for a conversion I'm working on - where can 
I find one for a reasonable price?  Used would be fine.