Harmonic Balancer options.

[hoffbug]

I have an Olds 215 ... Ive bought an adapter plate to mount a 200R4 transmission.. Part of that kit is a Buick 215 Flexplate that has been modified to work with a modern torque converter pattern. The rubber on the stock Olds balacer is cracked and dried out .

Are all Buick 215 and Olds 215's internally balanced?

If so what are the options for balancers out there? aftermarket? are Buick 231 balancers compatable?