Update
The CB450 Nighthawk turned out to be the best of the three. New tires, seat cover, boiled the tank and cleaned the carbs. Rebuilt the brakes. Replaced the mirrors, tail light and the levers. I spent lots of hours taking things apart and polishing plus repainted all the plastic and the tank. Runs and shifts great, I spent about $350 and gave it to my grandson.
I gave the 77 CB750K to a buddy and it is at the Limmie's in Austin. He is building a CR replica with full fairings. ROC City is fabricating a polished aluminum gas tank with the oil tank built in and fabricating the aluminum tail to conceal the battery. All the wires will go through the frame so it should look pretty clean. The motor is almost finished to an 836cc and it will probably be another 3-4 months before the build is finished. I said to my friend "so when you said you wanted to build a bike you meant write the check?"
The 75 CB750F is stripped to the last bolt. I rebuilt the carbs to get it running to make sure it shifted. The compression is okay, a bit lower in one hole so I am weighing the options (how far do I go) for a rebuild. I finished the mods to the frame and the forks and will send a bunch of stuff out for powder coat in the next few weeks. I have been rebuilding other components and gathering pieces, seat, rims, bars to complete the build but this time of year is a busy season for me and great riding weather so this will be a slow build.