Update and thank you!
Thanks, guys! I had the Luger checked out by a couple of people in the area. Details I found out (again, bear with me if this is elementary, as my prior knowledge of Lugers was minimal) include that it's a 1921 "DWM" commercial P08, 9mm caliber, 4" barrel, with matching numbers on frame and barrel. The bluing is about 85% (a little pitting here & there, mainly on the barrel and backstrap). The magazine appears to be non-original (stamped "Made in Holland" in English), and one of the grips is cracked. I got quoted a likely value of around $1400-1600 if the pistol sold on one of the auction websites; based on my internet browsings over the past few days, that seemed to be in the ballpark for its condition. When we next spoke, I told my friend that I wouldn't be able to afford to pay him what it was truly worth, and was about to give it back to him. He then surprised me by offering it to me for quite a bit less, stating that he was no collector, he could tell I really liked the piece, and he just wanted to see it go to a good home. It's restored some of my faith in humanity, I tell ya..........
Now, to look around for some replacement grips and put this baby to work! (Hope the camera phone pictures aren't too horrible.....)