Greetings,
My Father-in-law has a mix of Star and Phelps machines. In a parts box he does have a powder housing stamped "5/8". It is a casting, so I think it is an original Star or Phelps item. The parts are 20+ years old, long before replica items appeared.
There is also a mating brass powder bar stamped "20 gr 2400". Again, impossible to tell who machined it.
Cheers,
Dave