Rosebud, I went downstairs and took a look at my Contender…..a Gen II (I think) bought in early '90's, so the serial # location may be different on the Gen I's.
On mine, which has the original Pachmyar grips, if my memory serves me correctly ……his would have been drilled/tapped just below the serial #. My grips would have to have a small portion right at the top removed to access the frame just below the serial #.
In looking at mine, assuming that the frame grip area is identical on the Gen I's…..I'm assuming that he drilled/tapped at a downward angle, to give adequate clearance during recoil between the ring stud and the web of the shooter's hand!
I also can't remember if he still had the original grips or had replace d them with aftermarket!
I think that a friend of the family has the handgun, I'll try and find out….maybe I could get a photo of the modified area!
I'm sorry that I can't offer many concrete eye details!
memtb