For this swap, I had to ditch the M6 flywheel and get a automatic transmission style Flexplate. Because of the myriad of GM designs as far as crank, diameter, bolt pattern, etc you have to be specific when ordering the flexplate. I called and discussed the situation/setup with Dennis Smith at Internet Racer Supply and he recommended the Pioneer brand having 153 teeth but fitting the one piece seal crank that the LT1's have.
This is the box the flexplate came in with visible part number.