Oh, man, CB750R...I'm really sorry for you! I've had SO many bad ones like that over the years...
If the pistons are forged. they should be 0.0018"-0.0025" clearance.
If they are cast pistons, they should be 0.0008"-0.0012" at that bore size.
I always go to the lower number, myself.
I have asked automotive machine shops to bore sets of cylinders for my motorcycles;unfortunately they don't like to give what they consider to be "too tight" of clearances between the fit of the pistons and freshly bored/honed-to-fit cylinders.
1 out of 50 automotive machinists will bore to "only" .001"
.
I only look for 'powersports machine shops' for doing Japanese motorcycle work now.
I have found an experienced independent powersports machine shop out here who is accustomed to setting things up correctly.
I've slowly been learning to be patient with this machinist because he's very good at setting the finished product to my specification:according to factory specs in the manual.
This particular shop/machinist is in high demand among many motorcyclists
I asked him to set the finish hone on my previous piston-to-cylinders job to the low end of the scale at .0006" (the variance is .0006-.0018")on one of my Honda engines;it took a good amount of time for break-in on this particular engine and I'm very pleased with the performance of the engine and I expect it to last quite a few thousand miles,even at the high rpms I run it.
When I consider letting another machine shop do the work..
well.,the price to do the job twice/over again and hope it will be done 'to spec' is more than I can afford,especially after the sad first result.
I've been burned plenty on this issue.