30 cal WW1 broomhandle in 9mm serial range?

[DonVoigt]

Joe,
I believe you nailed it.
"Red 9"s are popular due to the military connection.

But,
I'm going to guess that your grips are replacements, as they are the wrong style and lack the Red 9 incised into the outside.
I don't like the look of the serial number on the left flat of the chamber either, looks like it was added to match the upper to the lower. Notice how close the top edge comes to the marking on the top flat, I believe the original number was milled off and a new number stamped.

I'm afraid you have a "boosted" 9mm Mauser, renumbered to match.

Post some hi-def pictures when you get it for a better look; these pictures won't expand enough to see fine detail.