Nope. Wish I could be of more help. I'm using that B-Square mount on an old mod 29 that was made prior to the drilling and tapping for the mounts on that series. I'm surprised that your 629 wasn't either drilled and tapped or that the mounts that use the holes under the rear sight won't work. That does leave you in a lurch!
Here's a link to a mod 629 Classic for sale, and which shows a B-Square mount and rings. You absolutely sure that the B-Square won't work?
http://www.gunsamerica.com/928127134...1_2_Barrel.htm
Can't see why one of these mounts wouldn't work.
http://www.brownells.com/.aspx/pid=1...EVOLVER_MOUNTS