904 behind 360

Your making this way harder than it needs to be. If you buy the B&M flexplate and use it you can swap in any neutral balanced converter the same diameter as the original you want at any time. It'll bolt right up and be balanced because balancing is the job of the B&M flexplate. That's why you put the B&M flex plate on, to get rid of the need for a specially balanced torque converter.

If you go with that E-bay torque converter it will work but if later on you want to upgrade to a higher stall you will have to again buy a specially balanced converter.