there is no difference in the flexplate , they are all neutral balanced , the external weighting is on the converter.
Your holes sizing is off , 5/16 or 7/16 I don't recall ever seeing a 6 bolt factory flexplate with 7/16 (hemi) size holes ... but I haven't seen every plate made for production line cars ... maybe a Direct Connection/MP flexplate has a 6 bolt crank flange and 7/16 holes ??
All 426 M.W. motors and maybe the 413 M.W motors had them with stock 11 inch converters, maybe some other later ones had them OEM like the 1969 440 A and B body M code motors, maybe not
