Heym has made rifles on various actions over the years - including Rugers from the USA. I know of one gentleman who wrote them to ask if they ever used Brno made ZG 47 receivers for any of their bolt rifles to which they replied - "Nein". I was able to produce pictures of two such rifles clearly marked Heym. Point made is don't put too much faith in their answers.

If you had access to several Mauser bolts, the chances are that one of them would headspace correctly.

JC