A999 Transmission mated to a 73 340 motor

Professor Fate said
Are you sure the A999 was from a 318 and not a 360?
I come up with a #10234 for an externally balanced 340 with a 904.
Mancini Racing - Balanced Flex Plate

I don't understand Mancini, $189 for so called balanced, when B&M has them for $119.

B&M doesn't balance them ? 10235 is correct for B&M

Flexplates - Holley