The T4's were offered up until '88 or so. Some were simply T5's with the OD gears removed, however most do not have the right tail shaft or internal shafts. They make good donors for a front case for a T5. Other than that, they are not worth much. I would NOT replace an SM420 with a T5. With your 250, I would be looking for a NV3500 from behind a 4.3 V6 in an S-10 Stronger than the T5, and will bolt up with NO modifications.
Scott
