Find a rear end from a 1969 Chevy 1/2 ton truck and it will fit in there just fine. Possibly earlier years (66, 67, 68) would also work. Wasn't until sometime in the 70s the width changed and then they went to 5 lug wheels. I have a 1969 in mine and unless you do something like use too large of wheels/tires, all will be jake and you'll have a 6 lug rear end. Be really careful to study the rear end ratios v the ratios in your T5 transmission. You can do something neat there or you can create a little over-geared or under-geared nightmare. Lots and lots has been written on that topic here. Let us know if you need help.
