Even if they're wrong, if they were made to fit with brackets that line everything up correctly, and they have adjustability to keep the proper pad to rotor clearance so you don't get premature wear, squeaks, and excess heat transfer to the rotor....and the calipers don't have too large a piston swept volume for your master cylinder to provide fluid to it, then you've got no problems other than you won't win any points in a restoration.
The brakes on these bikes were not that good to begin with, so i would start by comparing your braking to the braking of a similar bike if there's someone near you with one. If they're close, no worries. If yours is significantly, or even noticeably worse, then I would check out the caliper. If it's got a larger piston that stock, chances are the master cylinder can't keep up and you've got too little pressure being put on the pads.
Another possibility is the piston may be sticking in the caliper bore, That's something you can check by taking the caliper off the bracket and applying the brake lightly, if the pads close up it's likely not sticking.
I don't know what year yours is, but from what I can find online the 77-80 CB750F has 35mm x 38mm pistons, the 81-82 CB750F has 30mm x 35mm, and the 69-76 piston is Honda part number 45107-300-003 and the seal is 45108-300-003, (size is 38mm dia. x 34mm height)
That's probably not everything, but should get you started. Post a pic of your caliper too...this is what a '69-76 single front caliper looks like....well, some of the '69's were probably different, but most of the 70-76 SOHC should look like this....
Mark Davis
Palm Beach Gardens, FL
amateur photographer, hot rodder, motorcyclist, adventurer
"Four wheels move the body. Two wheels move the soul."
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