Ok, I was waiting for someone else to chime in.
I don't have the exact answer your looking for, but I do know that the '79cb750 front brakes mount right up to a '79cb650 fork.
My bike origionally had only one brake mount, and since I had 2 pairs of forks(both off '79cb650's), I was going to run with one brake set mounted correctly(behind the fork leg), and the other mounted in front instead in the back of the fork.
Looked FUNKY though.
That is until I measured a bit more, and found the fork sliders are the same diameter between the two bikes.
I used the CB650 sliders, and the '79cb750 forks and brakes.
I would have used the '79cb750DOHC sliders as well, except they measured an inch longer than my 650's.
So to keep the stock stance of the bike I opted for the orig. sliders.
Hope I have shed a glimmer of light for you.
l8r