You will have to get a 23 tooth. But watch out. Mine only lasted a few miles before it chewed itself up along with the plastic drive gear on my 96. I would recomend getting the 7 tooth drive gear from a cobra. Then you can use a standard driven gear(I forget what size gear you need) or just get a speedcal.
Well actually we swapped ours without removing the tranny. But I think it would be easier to just pull the transmission. But to answer your question. You do have to remove the tailshaft housing. Once that is off you just have to remove a large e ring to remove the gear. It was an easy swap just time consuming.