Pics would be a big help. Without seeing the bolt handle I wouldn't even hazard a guess. As for whether or not the side mount was installed by G&H, if they did it the screw heads will be flush with no slots showing. Ie: they installed them with extra long screw heads and pins and ground them flush before bluing, making them nearly invisible. That's not to say though that a conscientious smith wouldn't have done the same thing.