Digging into to this after discussions here, I've found that the 73 400 externally balanced motor has a 68 727 transmission with no weights on the converter and a stock bow tie flex plate. Now sounds like I can either buy the correct weights and weld them to the converter or replace the bow tie job with a weighted flex plate? Would seem the flex plate change would be the better option if I can get a correct one somewhere. B&M 10237 flex plate appears to be a good choice.

Hopefully the previous owner running this combo for years hasn't messed up something else in the motor. Probably not good on bearings.

Thanks for all the great input !!