Are the rotating parts, crank assembly, internal or external balanced?
If external make sure the converter has the weights on it to match your motor, if not don't worry about it.
I would look for and use a 11 inch stock converter for a big car like a C body or a 2 barrel B body BB motor
I'm talking about a converter that would foot stall from 2000 RPM up to a max of 2600 RPM and still work well at part light throttle driving