I don't see why it would be 96 only unless they changed something about the way the trans computer interfaces with the trans just for that year. I'm not 100% positive but I'm not aware of any changes in that year that could affect the ability to swap to a slightly older one. However my experience with the 604's is more with the early 90's stuff. I do know there was some internal revision made to the 604's at one point, but AFAIK it did not affect swapability.

Around here a junkyard 604 can be had for $100 or so at the local u-pull, and that comes w/ a 90 day warranty. If you can find one from a decent mileage car that looks like it was taken out in a crash, it's usually a better bet than the $$ for a rebuild.

Two small tips if you do get another trans, put an external trans cooler on it in addition to the one built into the rad. The o/d on these trans puts out a lot of heat and a trans cooler really extends the life of these units. Also make sure the shop uses chrysler atf+3 and NOT dexron/mercron.