I have contacted them before, and they really seem to know nothing about anything before maybe the mid 50's which they consider their modern era? Probably like all the others, their prewar info is obliterated. Most likely thing would be to see if you could find period advertising, maybe. But count yourself lucky having a Heym. Have you priced their current offerings?!
Your gun is like your nose, it is just wrong for someone else to pick it for you!