Hi Ian, I've struggled with the same issue and wanted to relay my experience. For the m/c I WOULD have gone to Sierra but they closed some time back So Instead I went to White Post restorations in Va and was very happy with results. I'd call to confirm they can address a stock Pantera m/c diameter if that's what you have. Mine was a non-stock 25.4mm (1.000") Benditalia unit that looks original and has exactly the same parts inside, only a few of larger dia. Had 2 similar masters done by them this year.
As for calipers I have had various sets of ATE & Girling calipers done at PMB Performance in Utah. Check out their website, they are ATE specialists and have connections with a great plating shop in their area. So they plate mounting hardware properly, too. It's been a few years now but hopefully they are as good now as they have been previously!
I've been very disappointed in mc/ sleeving work done by some other shops you would probably recognize so there could be a crap shoot element to this. Regards, Nate Stevens