all you need to do is use the rear half of the drive shaft to bolt the t18 diff in. Theoretically you should be able to put the s series diff back into the t18 as they should bolt across fine. Was thinking of doing this a while back. (buy a t18 for $500, swap diffs and re-sell t18 for $500) but I was able to get one from a wrecker so didn't bother.