Tune up.

You may need new fork springs. The manual has a spring free-length spec, so measure them.

Brake squeal. You can check the lining thickness of the pads to make sure they have enough braking material left on them. Apply disk brake grease to the backs of the pads (I use Permatex Ultra in the little packets). Each caliper should have a pad spring. Also, there should be little pad guides that can go missing, but I'm not sure if those have any effect on brake noise or not.

I've pulled them off once they look like this but worn lol

Just out of curiosity, what is the ideal rev range at that speed? I have an 82 KZ750-H3. I rarely go over 75mph which is about 6500rpms. Does that seem about right?

No. At 75 mph your engine should be turning less than 6,000 rpm (I believe somewhere around 5,600-5,700). As an example, my stock KZ650 turns 6,000 rpm at 80 mph. If you are using the stock sprocket sizes you either have a clutch that is slipping or an inaccurate tach and/or speedometer. Ed

Probably a combination of sprockets, I'm pretty sure they are not the stock sizes, and an old tach. I don't have an actual speedo. Just use gps when I feel the need to know how fast the bike is going lol.