360 727 converter question

Buying a newly rebuilt 727 and converter that was on a buddy's older Cuda (68) with a 340.

I researched but was fairly confused...but maybe I get what I need to do?

The 340 is most likely internally balanced, so the converter will be zero balance. I have read that some later 340's are externally balanced, however, the counter in that case would be done with the flexplate....both internal and external 340's would use same converter?

There is a B&M flexplate that will allow me to use the zero balance converter on my 360.

If I have this wrong, do not be shy. I tried my best to search and understand but this is so different from the old dark world of Chevy and Ford that I am from (and even then I know enough to only be dangerous)

Thanks!