You got the right flexplate on ? Found out the hard way with my friends 351W that when he swapped the trans of his 302 Cleveland, he swapped torque converter flexplate and all. It all bolted in but the clearances were wrong and it locked the motor up tight, apparantly the cross section of a 302C flexplate is thicker in dimension.

Dont know if this awnsers your question but boy oh bopy it was a learning curve for us.