Front fork

To retain that oldskool look I wanted to fit a set of shortened GSX1100 forks instead of modern Upside-Down stuff.
My first choice were GSX1100ET forks which look great with their leading-axle and don't have the troublesome early anti-dive system. The pair I got had heavily pitted stanchions so I went looking for replacements. A quick browse through an on-line parts catalog revealed that the GS500 also has 37mm stanchions which are 66mm shorter and seemed great for my purpose.

Stock GSX1100 fork tubes: 37 x 671mm
GSX1100E tubes: 37 x 590mm
GSX1100EF tubes: 37 x 596mm
GS500E tubes: 37 x 605mm

I found and bought a set of used GS500E forks, and when I test-fitted them I thought by myself "mmhh... these are perfect by themselves... clean looking, lightwieght, allmost short enough and a single caliper mount". So I decided to use them completely, albeit shortened by 30mm.

btw. You can't use the GS500E stanchions in the GSX1100 fork legs because they're thinner i.e. have a bigger inner diameter.
This is the geometry I'm aiming at with the front axle, swingarm pivot and reax axle in line with each other.
Picture shows compressed GSX1100 forks.
The GS500 forks use a 180mm spacer between the preload adjusters (21) and the spring (17). By shortening these and adding the same amount on top of the rebound spring (13) you effectively shorten the forks by decreasing the suspension travel.
Upper side of picture shows the stock inner workings.
Lower side shows the shortened upper tube and the spacer between the damper rod and the rebound spring.
This is the difference between GSX1100 forks and the shortened GS500E forks.
And here's the setup with a piece of string between the front- and rear axles to show the alignment.