I believe the reason more people aren't using the T56 is because the shifter location is so far back... about 23 inches from the bellhousing. Take the stock 4 speed with the shift tower coming up at 4.5 inches from the bellhousing, and you can imagine the problem with seat clearance. The T5s with the S10 tailhousings shift a little bit further forward than the other T5 transmissions making them an ideal swap in an older truck with a small cab.

John