Flex Plate?

LA and Magnum are external balance but different weight. B&M Magnum to 727 used with a 904 bolts up but the starter will hit the edge of the flexplate when you try to install it.
I ran a OEM with one elongated hole, 7/16 bolts high 11s 1.65 60' with no problem. After you elongate the unsymmetrical hole you can weld up the open side and dress it up.