The 75-77 GL1000 rear master and rotor are a direct swap to the SOHC F bikes.
The F0/F1 uses a unique rear caliper that I don't think Honda used on any other bike, it's actually pretty sophisticated for 1975, a fixed caliper with twin opposed pistons. The F2/3 uses the same rear caliper as the Goldwing, a single piston sliding caliper.
I ended up putting an F2 caliper and bracket on my F1 (you have to get the caliper bracket too, the later caliper won't work with the early bracket), which meant a new hose because the 2/3 hose is longer than the 0/1. Other than the hose length it's a bolt on swap and you can re-use the existing caliper stay.
Here are a couple pic's of mine, first as I got it, and as it is now. I had to replace a rusty tank and muffler and cracked side covers