Jack,
Is there a chance of seeing three more photos :
1. View of entire gun barrel... a 6" barrel on an M1900 AE is not usual.
2. Detailed photo of the barrel/receiver witness marks.
3. Detailed photo of the polished area underneath the thumb safety lever.
By the looks of it, I would vote for this luger being professionally (possibly recently) redone...but more photos would cetainly help.
The lack of depth of the AE chamber stamping is one "red flag"...
AZ state certainly has it share of boosted lugers showing up...