FWIW, Talley would tell you not to lap those rings. Partly, out of pride. Mostly because of their design. With most rings, you can firmly anchor the bottom half to the base or receiver. Then the top half is mounted with a 'soft' fit around the lapping bar. The vertical rings will tighten on to the base and bar/scope simultaneously. Not saying it can't be done, mind you. However, somewhat doubtful on the odds of success. Where to source a 34mm bar? No idea, as I have never had the bingo shells for a tube that big!

If you have access to a lathe, it would not take too much to turn down a 1 3/8" (34.9 mm) shaft.