Do yourself a GIANT favor and call a reputable converter company with all of the info that you've put here. Converters aren't Voodoo, but darn close IMO. FTI, Hughes, PTC, Freakshow, Circle D, etc. My son has a low stall FTI in front of a 200-4R that is absolutely sick on the street. I have a Freakshow that I really like in front of a 4L80.
There is a crap ton of design in the stator differences, a converter for a 300hp NA motor is wildly different than one for a 400hpo with a 200 shot of nitrous.
There is a crap ton of design in the stator differences, a converter for a 300hp NA motor is wildly different than one for a 400hpo with a 200 shot of nitrous.