great question. something I've been wanting to do for awhile. i hate the shift pattern.
t50 shift pattern
R 2 4
1 3 5
t5 shift pattern
1 3 5
2 4 R
here is some of what i know.
olds bell housing are all the same, they are a BOP housing with a dual transmission bolt pattern. the first pattern is for traditional muncie/saginaw/t5. the second pattern is for the ford HD 3speed trans that was offered back in the 60's. both of my t50 equipped cutlasses have this bell housing.
the t5 is the hard part. t5 trans from gm came in several configurations. the f body trans from the 80's were either a v8 with 26 spline input shaft or a v6/4cylinder 14 spline input shaft. the v8 trans have the correct input shaft length where as the other input shaft is 5/8" too long. this added length can be correct with either a saw or a spacer plate.
also, the f body trans were rotated counter-clockwise 17 degrees and is reflected in the bell housing and in the trans mount. when bolted to the olds bell housing, the trans mount is now rotated 17 degrees clockwise. a custom adapter needs to be fabricated because of this angle.
starting in about 88-89, speed-o-meter cables were replaced with vehicle speed sensors.
now, can you mount the t5 at the 17 degrees twist like the f body, maybe, but you may not have enough material on the bell housing or a rib may be in the way.
can you mount a ford t5 and use the ford pattern, no, it doesn't match. ford changed their trans patterns like a teenage girl changes outfits.
then there is the gear ratios, v8s have the best gearing. v6s are about the same as the t50.
i'm not sure if the t5 shifter has the same location as the t50, but it will be close.
next up is the t5 from the s10 trucks. these trans are mounted in the normal up right position, but the shifter is mounted in the middle of the trans, compared to the f body which is at the end of the trans. i think you could make this shifter location work, butt does not fit in the factory g body locations.
these trans follow the f body trans with similar v6 gearing and speed-o-meter cables and input shaft length.
clutch disc would need to match trans input shaft and driveshaft length may need to be adjusted.
all t5 trans starting in about 93, f body and s10, switched to the ford pattern. f body trans continued with the rotated trans and the s10s still had the mid shift shifter location.
i'm plan is to try the t5 from a v6 firebird, i will redrill the trans pattern on the bell housing and may have to add material for trans to bell housing mounting bolts. it has the speed-o-meter cable. change the clutch disc, install my new hurst shifter. i'm not sure if i will modify the input shift length or buy a spacer from bendtsen.com and adjust driveshaft.
joe