I have a friend who wants my 700R4 and I want his T56. Thing is, he has a 2000 LS1 T56 and I have a '93 LT1 700R4 (4L60).

What would have to be modified on both cars to make this swap work?

 

If I am not mistaken, I believe the input shaft on the ls1 is longer.

 

The LS1 T56 is designed to accomodate a conventional "pusher" type clutch. It has provisions on the front cover plate to mount the slave cylinder, which mounts concentric with the input shaft. The bell-housing has a hole for the hydraulic line.

The LT1 T56 uses the unique "pull back" clutch. It has a pivot "T" screwed into the front cover plate, and requires a dedicated bell-housing to mount the slave cylinder.

If you got the complete LS1 T56 assembly.... bellousing, flywheel, clutch, hydraulics and trans, it may be possible to adapt it, and have a much larger choice of clutches than you would have with the LT1 T56 setup. You need to find someone who has actually done it, to make sure everything fits. If the LS1 input shaft is longer, the bell-housing may also be longer, and that might push the assembly back far enough to cause a driveshaft length issue,. Just guessing on that part though.