68 slant six trans to 64 225 slant six

I put a 72 Dart drivetrain in my 65 Barracuda. I shortened the driveshaft about 3 inches since the Dart was a longer wheelbase. I also changed oil pans and installed a B&M shifter that fit in the console. If you want to stick with the original trans one of the trans vendors makes a bushing to fit the early convertor to the later crank.
Uhmm, You're bassackwards from what the OP is attempting, They're going early crank to late trans.