I put a internally balanced 408 in my 73RR & had to buy a new T/C because it had weights on it. Do I need to buy a new flex plate?

 

No on the flex plate. If the engine was not balanced with the damper on and it was a exterally ballanced damper you will need to replace it also.

 

I'm confused some people say I need a new flexplate & some say I don't.
B&M says I need 1

 

if it is internally balanced, you do not need a weighted flex plate or converter, if its externally balanced you will need a weighted flex plate or converter. if you put a weighted converter on a internally balanced engine, you will need to replace the bearings after start up., and probably a new tranny.

 

The old flex plate should be fine. The weights are on the converter. You probably could have taken the weights off of the old converter and been fine.