Your probably barking up the wrong tree by asking the dealer about your PCM
If I understand the 8.1L, it uses the same reluctor wheel, coil on plug and cam sensor that the LS motors use. I shouldn't be much of a problem to edit out the cats and make your nuisance CELs go away. If it has VATS that can be edited out too.
I'd start by looking for a local tuner that has the LS1Edit or HPTuner software. Any shop with an engine dyno will have a list of tuners that use their facilities and tell you which ones tune GM engines (if they don't have it themselves).
There's plenty of mail-order tuners too. Texas Speed and Marine comes to mind and I've used them a few times for LS engines. Just search "mail order tune 8.1" on Google to find ones that'll do the 8.1 PCM. Most of these places have an order sheet that will tell you what they can edit, including the cats.
If you're confident about your wiring harness stand-alone modifications, you may not need it, but LT1tech.com has some useful instructions on how to modify LS-style harnesses. He also does mail order tuning and it'd be worth asking him about the 8.1. His name is Brandon.
