The Z28 never came from the factory with a Borg and Beck 3 finger style pressure plate. They all came with a Diaphragm style, 10.5" in diameter, with Borg and Beck being one of the suppliers.
The model 1506 is a Borg and Beck 3 finger style pressure plate manufactured for Chrysler back in the 1950's and 1960's (and probably the 1970's), but was also manufactured by several aftermarket companies (i.e. Hays, McLeod, etc...) as a replacement for any engine using a 10.5" clutch.
I don't know anything about Perfection American (although there IS a company called Perfection Gear Company in Harvey Ill), so I can't say if it's original. They "may" have supplied discs to Borg and Beck in the 1960's but I just don't know.
Can you post some pictures?
Ed