4l60e tranny to LS1
Changing the trans is not a reasonable option as it will require a rebuild and many parts including input drum with shaft, pump and bell housing.
Instead, use a 298mm converter (called an LT1 converter), a spacer on the flexplate to extend the pilot hole and longer crank bolts for the spacer. You may also need to elongate the converter holes in the flexplate. All this has been covered dozens of times here in just the last year.





