Superbee, I would be inclined to go with my gut instincts on that rifle. Personally I feel that it's the real thing. Germans loved to stamp everything with swastikas and waffenampts from 1936 to 1945. They stamped just about everything they managed to get to a rear facility.
Go with it and give it a good home. The previous owner knows his stuff, better than just about anyone I know. He is reliable, honest and credible. Always has been, since I first met him 20+ years ago. I doubt that anything has changed. If anyone has had the opportunity to ferret out rarities, he would be the one. After all, he's had access to several thousands of them. Many of which he inspected personally. We should all be so lucky.