I thought the difference between the early and late Magnum flexplates was the early plate had an asymmetricical converter bolt pattern, and the late plate had a symmetrical bolt pattern

1969 Nova
454/M21/3.31
Mild mid-11 second weekend cruiser

1994 F150 XLT Super Cab 2WD
5.0/4R70W/3.55
(Daily driver)