GM puts a paper tag on it near the converter hub. Example of the code: CG3C. There are many other codes as these converters were used in the 200C, 2004R, and the 325-4L. Factory codes for Turbos and HP, would be CB4C, CB5C, CF9C. These were a 12" (298mm) diameter converter.
You'll have to pull the converter out to see the tag if it's still there. Your converter looks like an original factory unit as it doesn't appear to have been painted. Almost all converter rebuilders from my past experience paint their converters. If the tag is still there, let me know what code is on it.
Flash stall isn't when you hold the brake, that is a brake stand. It is the rpm the tach jumps to before the car moves when you floor it, at launch. Yeah, governor mods are needed. I had one shift a 3000 rpm, awful. Your cam is just getting into the powerband.