LT1 4L60E Question
He needs a '96 or '97 trans OR a '98+ from a V6 engine, which will have a 298mm input shaft and NO bolt hole at the 12 O'clock position. You are correct that a trans from an LS engine will not work.
Avoid any '93/'94 and '95 as these are very year-specific and electrically incompatible with any other year.
IMHO '93/'94 was an Alpha-test, '95 was a Beta-test and it wasn't until '96 that GM finally figured out how to electronically control the trans. No further electrical changes were made until '05/'06 when ISS (Input Speed Sensor) was added and even that is not incompatible. Around '08 significant changes were again made which are incompatible with earlier years.





