Slides are scarce. Numrich has 2, 3rd series (find ser no range) that requires no bushing. For $101 & 130
https://www.gunpartscorp.com/products/1234920
https://www.gunpartscorp.com/products/1269530
Found a discussion containing ideas and conjecture and a "how to" that seems painful and leaves the lock indicator in the trash can. Have looked everywhere including Glock Talk. I gather it would be one PITA and paying a 'smith would add $ to your oveall purchase...
Hold the pistol as you would shoot it with your index finger laying along barrel. Pick a spot on the wall as your target and as you bring it up close your eyes and point finger at target. the 1 with sights aligned with target is the 1 you want.
The shotgun that fit me perfectly was the 1968 Rem 1100. I find today's rendition has a pull of 4.9. I no longer have it, so can't measure it. Used it for dove hunting. My memory tells me it was lighter than 4.9. Maybe today's safety factor.
Here's an article...
A tete a tete meeting should alleviate any fear of scam. Unless he has an accomplice hiding in the cane. I always do that for local buys. Meet in the WM gas station parking lot away from prying eyes and you should be OK.
Perhaps he is antsy about people knowing he has that many guns. He is also...
Looked up some reviews and your results seem to be common to non-existent. About 50-50. One person had 5 duds in a box of 50. Others have no problem. Others had the light primer strikes. This was from a myriad of different pistols