Can't speak for the F model wheels, but the K series wheel outer doesn't have any sort of mounting for the cable sheathing. Essentially, you're looking at either extensive modification to the outer plate - and almost certainly modding the rear lever and it's spindle and the length of the bar that stops the outer rotating (sorry - can't think of the name of it right now) - or using a wheel from another bike.
The 750 was essentially a scaled-up CB450, so they share similar component design (i.e. rear brake linkage). As far as I can tell, the biggest bike of the same period - early '70's - that Honda used a cable on was the SL350 ('69-'72 models). And before you ask, no, it wouldn't be a good idea using one of those wheels - not only are they unlikely to be able to cope with the weight of the 750, they're 18 spoke (instead of the 750's 20) and they're crazy scarce over here. Even if you can find a wheel, the brake cables are almost impossible to find in any condition, although I guess you could get an aftermarket cable made up.
Having said all that, you might find this sort of mod has been done by some of the race boys in the US. I'm assuming you've checked out the US SOHC forum . . .
Hope that helps
