I replaced the stereo in my 96 2100SR. According to the parts guide for yours, it is the same stereo. So mine was the old 2 post style (1 post for volume and 1 for tuning). If yours is the same, you have to pull the knobs off and then pull the nuts off the posts. Then remove the back bracket and it should come right out of the back side. I was not able to find a harness adapter so I just cut it off and spliced the wires in with heat-shrinkable butt splices.
So my new stereo was a DIN mount. So I have to use a straight blade hacksaw and cut out the panel opening so the DIN mount fit into it. It was a pain but does work nicely now. I also replaced my speakers with Polk Audio 5-1/4 db521 series. Had to cut the opening just a bit bigger to fit them but just a trimming. Not nearly as much as putting in 6-1/2 speakers. I then added 2 more speakers above the grab handles between the front facing rear jump seat and the rear facing convertible seats.