I have just had a couple of 2 3/4 Hp barrels bored out to suit new JP pistons by Beaudesert Engine Reconditioners and I pleased with the results.
The service was very prompt (two day turn around) and helpful. Reasonable rates ($200 for two barrels and valve reseated) They specialise in vintage cars and motorcycles and one of the few I have found that can do blind barrels.
Contact:- Beaudesert Engine Reconditioners, Karl Rowlands, 07 5541 0590