Quote: ...it's entirely plausible to think that someone of that time (1937) may have crafted, or ordered to be built by a guild shop, a'custom' Mauser that varied considerably from the Mauser factory styles.
Absolutely! Even Westley Richards offered Mauser '98s with slab sided stocking. Very much a German, or even broader European style but even the English weren't averse to satisfying a customer request.