550 forks work better with the 550 then the 750 forks. put in some preload spacers and some new oil and fork seals and youll have all the performance you need.
you can use those calipers but youll need to create a custom bracket.
only newer calipers that will work are either if you get a front end off a gold wing (great front end) or if you get some sweet ass custom pretech calipers with slim backs so they clear the spokes (what im in the process of doing... kinda pricy, super amazing good looks plus amazing stopping power (6 piston!)... have to order them from england plus they dont make a caliper that mounts to the forks exactly (but they may be, ill keep you posted on what they tell me) so a custom bracket is necessary again).
you could also mount a new rotor from ebc... floating and awesome.
only limit is budget and what you can do with your hands. Stainless steel brake lines are a must. Ive been spending a lot of time on figuring out brake upgrades for the cb450-750 line up and this is what ive come up with so far.
good luck with the build!