Hello Luke,
I cannot tell for sure, but it appears your grip screw(s) are not Erfurt proofed. If they are, they would have a similar but smaller version of the Erfurt proofs that appear on the trigger side plate and the take-down lever, and many other small parts on your gun.
I am not sure how much, if any, these grip screws detract from your pistol's value...
Since your pistol has such a family connection, I would personally not worry to much about screws or a renumbered magazine...
Regards,
Pete... <img border="0" alt="[typing]" title="" src="graemlins/yltype.gif" />