P.S.
Some of the 3rd Gens have Novak dovetail cuts.
I have to wonder if this EGW Novak cut plate would work?
adapter plate
I know....it's not going to mount a Vortex Viper, but I've been wanting to try a Holosun 507c which has gotten very good reviews.
My 'ol eyes are about done with iron sights and I've gone pretty much all-in with Red Dots except my pocket pistols.
Once I got past the learning curve; they're just so much faster and more accurate for me. It's kept me in the game.