Mike,
If it helps, Heym made the Model 2,000 , 3,000 , and 4,000 Mauser rifles during the same time period. If you can find photos of these rifles to compare to yours, it may help. Also, if you post photos of your rifle someone may recognize it. BTY, because of factories in the area, including Heym in Muennrstadt, the Munich proof house had a sub-facility at Mellrichstadt. Your rifle was likely proofed there, they used the Munich house mark. The Heym made Mauser actions of that period had a tubular receiver with the recoil lug welded on. This was different than the Mauser 98 so would serve as an identifier for you. Waffen Frankonia had an "in house" shop that built sporting rifles from surplus mod. 98s, if your rifle doesn't have the Heym type receiver it might be one of these.
Mike
