If you're getting another transmission, you should go ahead and get the 80e that matches your flexplate. Be cautious, though, the later 80e convertor mates to a dished flex plate with the short crank rather than the flat plate with the long flexplate. Some of the 6L engines have a bolt on extension on the crank rather than an actually longer crank. You should pull the flexplate off the engine and see if you have the removable spacer, it will open up your options if you do have the spacer.