Thoughts on early vs. late Slants.

Different pilot size, I thought?
No sir. The pilot bushing is the same. The difference is the crankshaft register where the flywheel/flexplate mounts. I believe the split is 68 and up is the larger crank register and 67 and prior is the smaller. So you have to use the matching flywheel/flexplate/torque converter for the given crankshaft register size.