EBC makes rotors for the 1979-1982 CB750/900/1100F under their Pro-Lite brand. They are pricy (I think almost $200 per rotor). Those rotors will fit the 77-78 cb750F, I use DOHC rotors all the time.
http://www.motorcycle-superstore.com/11089/i/ebc-pro-lite-front-brake-rotorThe weak link in the 1977-1980 (SOHC and DOHC) brake system is the rotor. The solid type stock rotors....
...are prone to warping fairly easy with hard street or track day use. I have thrown away at least a dozen warped rotors on these bikes over the years. They are too thin to be cut, so once they warp the are pretty much done.
The 1981-83 style rotors....
...had cooling slots added to them around the inner circumference to prevent warping. It is still possible to warp them, but they are less prone to it. I used to pick these up cheap ($20 a set or less) and swap them on to any bike I had that would take them. The dual piston calipers that are paired to these rotors stock help as well by providing a bigger brake pad surface area so there is less heat buildup.
The warping problem comes from a variety of factors: with the single puck calipers the pads are too small, the rotor diameter is too small, and the rotor is slightly too thin for the speeds and heat it sees (modern rotors are actually as thin or thinner, but are often almost twice the diameter).
Now there are some other options as well in the OEM honda parts bin:
Honda CBX Pro-Links (1981-82) as well as CB1100R's use this rotor:
It is a vented rotor with direction cooling vanes. This rotor is bolt on for any 5 bolt comstar bolt pattern, the down side is you have to use the dual piston corresponding calipers and brackets that go with these rotors. Why is that a down side - well they are CBX parts only which means they are usually rare and expensive. Every time I see these rotors up for sale they are usually moving for $250, and that is before you track down the correct calipers and brackets. They weren't used on any other model except the cb1100R which was not sold in the US and usually carries it's own premium for brake parts.
Some VFR options work as well since overseas (non-US) VFRs used comstar wheels, but I don't know off hand. The important thing to look for is that 5 bolt pattern in the rotor as some VFR's use a different bolt pattern.
In terms of calipers the cheap and easy swap is DOHC cb750/900/1100 F model 1981-82 dual piston calipers. I usually find these in junkyards frequently - the brackets are harder to find than the calipers since they used the caliper body on a ton of bikes, but the brackets on only a few.
In terms of aftermarket calipers, the only company I know that may be supplying calipers that would fit the 1977-78 cb750F is Beringer brakes:
http://aftermarket.beringer-brakes.com/en/They offer 4 and 6 piston setups but their site doesn't specify years so it is hard to confirm, although my friend who is a beringer dealer here in the US tells me they do. He also tells me that for a soup to nuts setup it will easily cross the $1000 threshold, and honestly those are really great brakes but the parts bin mashup stuff I have been doing for years has worked so well and usually doesn't cost me more than $250 with new braided lines and a master.
