I picked up a Leupold mount for factory d&t'd pistols in hopes that it would work on my 629 (didnt know the dash # before I bought it), and if it didnt it would at least work on my 617.

Obviously, when the 629-2 came in I saw that my mount wont work. What are my options at this point? Any other mounts that would work, or have a gunsmith D&T the holes?

What about the rib on the barrel? Its a 8 3/8" barrel, and I swear it looks like a scope mount rib on the top of the full underlug barrel.

This maybe your only option. No-Tap Weaver-Style Base S&W N-Frame Matte

I used it and I just didn't like the weight of the pistol with the scope, etc. But YMMV.

I may have some good news for you. According to my SCSW the 629-2 with an 8 3/8 inch barrel featured a barrel with integral scope mount for the S&W mounting system. What this means is that what you should do is start looking for some mounting rings that will fit the S&W mounting rail on the barrel. I would suggest trying a call to S&W Customer Service, they may be able to direct you to someone who still makes mounting rings for this mount.