when I put a cast crank 400 together the balanced flexplate was indeed different than 360 balanced flexplate. B&M offers both. Imho it's easier to deal with than balanced converters when later changing engines or converters.
I agree easier. I have decades ago used the mopar weights that are welded to the convertor. who knows ,...I might find a good 400 trans/convertor!!!
bad part is I buy parts NOW I have thrown away decades ago!! not to mention see people restoring cars that back then were not even considered "parts" cars!!! lol