Lowering a 1977 r100rs

A small point perhaps but I believe that a persons inseam measurement is a much better way to see & describe the problem than their overall height is.

True on that because I'm 5'-6" and I have nearly a 30" inseam. I can ride my stock height 76 R100RS or 94 R1100RS with no issues about reaching the ground at stops. Granted if both feet are down its just on the balls of my feet/boots. Either bike I can easily flat foot my left foot to the ground for stops and holding up the bike.

lowering

Definitely inseam. When you stop and you have long enough legs you set up a brace with your feet on the ground and your butt on the saddle and can keep the bike pretty much vertical. When you're on your tip toes you have to lean the bike to touch down. When the bike starts to go over you have a little ways to go before you can set up the brace and sometimes, such as on a slope or uneven ground, you can't get it done in time and the bike just keeps on going down.

Lowered my wife's /6 years ago. Narrowed and took out some seat foam. Actually put in some new stuff. The narrowing did help quite a bit. If you have the Corbin, it's a lot wider and higher on the outside edges than stock. Still wasn't low enough for her. I then cut, maybe an inch or so, can't quite remember, off of the fork springs and cut a similar amount from the shock springs. Anyway, the bike sat like normal, just lower. Handled fine and only had bottoming problems if we rode 2 up. Twisted the shocks all the way up and she was fine.

Now, on my bike, I got it jacked up a little higher than a GS. I figure if a sidestand on one side holds up a bike, why not one leg? Otherwise, I'm on tippytoes.

Before you alter anything might I suggest that perhaps a smaller/shorter person might find it satisfactory to ride with the shock spring adjustment at it's softest setting or so.

It also strikes me that when I use the proper size tires 3.25 X 19 & 4.00 X 18, the bike seems to sit a bit taller than when using the metric so called equivalent 90 X 19 & 110 or 120 X 18.

Further if you are fortunate enough to have a shoe repair craftsman nearby (rare these days) he should be able to increase the sole & heel thickness on a pair of real leather repairable boots (Red Wing or Chippewa for example) or some equestrian ones.

Diamond gusset jeans might just let the legs position themselves a bit for better function. Don't forget to provide some type of armor if not in real riding pants.

Each of these might yield an inch or so, which all together might just do the trick.