Re: 1986 750 forks: home made special tools?
417cc SAE 15 according to the Clymer manual. Or oil level of 159mm (completely compressed without spring).
Yes it is for down the fork leg. It can be a real prick of a job as the bolt is torqued to 55-70nm and as you've discovered the damper rod will rotate. Go make the tool above, or rattle gun - you'll also find homebrew solutions involving wooden dowels/broom handles as friction devices. I needed rattle gun for one leg both to undo and do up again.
Whatever option you take make sure you clean them out, doesn't take much to block an orifice.
If you're only doing the oil & seals you can do it without dismantling the lowers, by overfilling the forks with oil removing the dust seals + circlip and compressing them until the seals pop up the stanchions.
Or don't fill, take dust + circlip carefully pierce them and pick them out, hollow pvc pipe of correct diameter will drive the new seals home. Lots of ways to skin a cat, some more sketchy than others.