Despite what the naysayers have said, I finally got a chance to play with my new frame and forks.
74 CB550.
Don't have pictures or measurements exactly, but eye-ballin it up, everything is going to essentially bolt right up with the right bearings (which I have and will also list).
So it's exciting.
However, if the 750 steering stem is longer than the 550 then I don't see it working out quite as nicely. Without having a 750 handy I can't confirm nor deny that.
Pics tomorrow!