Far as I can tell, stock GMC could be had with 3 sp SM318, 3 sp SM320 (T85) or a 4sp SM420. (or a "Hydro"). Some of these transmission depend on if it was a 6 or 8. I believe all these were offered by Chevy, That means the bell housing should fit a Chevy engine as has been said. Don't know if a T5 fits where those trannys fit. Probably does. It does not mean input and output splines/shafts will work with whatever you are doing. It is possible that they were different for GMC vs Chevy. Starter mounting and flywheel need to be studied also depending on if you switch bell housings and trannies around with a 270. Just do your homework and take it all apart and be sure what you have or post pics of what you have or numbers.

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