Finally the decision has been made.

for the rear esternal weight, you can either buy a B&M plate that has a bite out of it at the right spot, or weld a weight on the plate or converter at the right spot(s).

Here is the B&M plate for 904/360:
B&M Flexplates 10239

You you can buy separate weights, and tack weld them onto the TC in certain spots. TCI has some info on that but there are better diagrams around.

The damper is a separate imbalanced part for the 360 to provide the correct external balance weight at the front.