keep the torque converter? (360 swap)

internally balanced engine has
-neutral balanced converter
-neutral balanced flex plate
-forged crank
-neutral balanced harmonic balancer

external balanced engine has
-cast crank
-harmonic balancer marked "cast crank only" with an eccentric looking lip on it

-torque converter has balance weights and flex plate is neutral (stock setup)
OR
-torque converter is neutral balanced (no weights on it) and you get a b&m flexplate with a notch cut out

so the benefit of having the b&m flexplate is that you get a lot more choices for torque converters.