Bound to be someone around you that does bike engines, I would ask a local bike club for reconsiderations.
Much easier to be able to go and see them if there's a problem and provided you take in the relevant BSA service sheet for regrinds they should be able to do all you need.
I get mine done locally and so far been good although a friend up the roads bike nipped up , looks like re-bored to tight, he's taken it back and they will check it and put right for free, would have been a bit of hassle had it to have been mailed.