I opened my Taurus 44 mag up from .427 or so to .431 for a .430 barrel with a cylinder reamer loaned to me by a member here. It wasn't difficult and was a great improvement!
I don't know if I'd worry about going from .429 to .430 though...
There is a company that will ream the cylinder for you and has gotten good reviews here. I'm sure somebody with a better memory will chime in with the info.