Both forks are 35mm diameter so they will interchange at the trees. The 77/78 F models run dual discs with trailing (rather than the K bikes leading type) calipers and their rotors are a different diameter, thickness and offset from the spoked wheels 750s rotors. These rotors are also a different bolt pattern than the spoked wheel rotors so you can't bolt the F rotors to the spoked wheels. Basically unless you want to do some "major mods" you will need to use the Fs comstar wheel to make use of those F forks. Search under "dual disc conversion" "GL1000 front end" etc etc for more info. This subject has been gone over a number of times . . . .
