What is the difference between the cadillac / aurora pcm's by year?
I know the Cadillac pcm will control the 4.0 and vice versa.
Will the different years interchange? example can I use a 2002 computer in my 1996 or 97 if I were to use an engine from those years and will it even connect to the existing harness?
Just curious I have access to a newer engine and computer just checking to see what my options are when my motor calls it quits...

Take a look at car-part.com and see what PN's they list, probably same. Also shows year to year interchange, just write down what years you see from part to part. Takes a little study, but often very revealing.

I guess what I was asking is will the newer pcm work with some of the older electronics like the bcm, the dic and the radio and so on. I know it would take tons of re-wiring but that is no problem for me.

I don't know if anyone has ever dug to find out.

GM uses a bus architecture and sends many commands to things like DIC and radio and such (depending on year) as a Class2 or CAN bus command. So the answer is grey. Will the PCM send it? don't know, if it isn't designed to chatter with a Cadillac device that isn't on a BOP, then likely no. But could it? Very possibly.

One thing certain between 2000 and earlier is the two different ignition systems. I'll bet a 2002 PCM will not drive a 96-97 ICM waste spark system. For starters the CKP's (CranKshaft Position sensor) and crank reluctor wheels are very different.