OK guys, I have some data I've collected around here that doesn't match up, so i just want to post my own experiences to clear up problems for future questions.
I wanted to replace the PCM on a 92 Deville that I've been working on here. I was told that the PCM's were all the same from '90 to '95. Since I had a spare for a '95 4.9 Deville here, I thought I'd swap it out.
While swapping it out, I noticed the Serv. number being different between the two. The '95 was 16196347 while the original '92 ended in was XXXX2240, which I thought was the norm from '90-'95 like I had heard.
Well I got it installed and had a no-start scenario due to a VATS problem. Apparently there's VATS info stored in the PCM, or at least some VATS info that changed in the '94-'95 models, probably necessitating the change in part numbers that I noticed.
But it's all ok, easily fixable.
A little research told me that some passkey info is stored in the EPROM of the PCM. Fortunately, in the 2240 style PCM, the EPROM is removable and replacable, so that's exactly what I did. I put up some pictures to show how it's done. There is a removable cover just above the label on the PCM. Remove the cover and you see the EPROM. It goes in and out like a stick of RAM on a computer motherboard. Just push the two tabs down and pull the EPROM out. I took the '95 PCM with good known injector drivers, replaced the EPROM with the original '92, and put the good PCM in the car.
So, for any future PCM swappers, if you have a passkey problem after replacing the PCM, swap out the original EPROM into a good PCM and you should be good to go