Brycegp.
You are doing it wrong.
#1 you can't use gl1100 calipers with cb750 rotors for two reasons: 1) the spacing is different, 2) The rotor thickness is different.
#2 you can't use gl1100 rotors with a cb750 hub because the bolt pattern is different. There may be some Honda spoked wheels with a 5 lug pattern like the comstars use, but I don't know what they are, maybe 1981-82 750k?
#3 you can't use earlier calipers or 750 calipers on the 80 fork legs because the caliper mounting spacing is different.
Let's start over:
To use your gl1100 forks you need the gl1100 calipers, rotors, axle, spacers, speedo drive, and a 5bolt pattern wheel (which will probably be a comstar). You will also need the gl1000 trees but be forewarned you need to find out if your fork diameter is 37mm. I am guessing it is not since it shares a part number on the fork seals with the cb1100f (39mm forks).
The better way to do this is to buy a 75-77 Gl1000 front end complete. It will cost you less and bolts right up. If you want to save on shipping you can reuse your cb750 wheel only.
Don't buy it piecemeal buys complete front end. You will have to rebuild and service th thing anyway, don't turn a $250 front end into a$500 one because the bolts and hardware nickel and dimed you.
I know you don't want to hear this but for what you want to do those 1980 gl1100 forks are useless to you. Sell them and buy the right parts.