The vin number matching up is important if you have warranty left on the car.
That is something the dealership may check when doing warranty work, if it does not match, they will stop working on the car, and ask questions.

You can get a used pcm, and you should be fine, there is no programming required.
I dunno if you will need to do the security relearn or not on a 1996, but that is all you would need to do.

If you get a new PCM from the dealership, it's like buying a brand new hard drive in the box, it is blank, they have to program it.