Digging your thread.I own 4 GS500s and have two spare frames.I have done a lot of mods on my 89 GS.It's designated a GSX500F.
You could have used the katana 600/750 front end, with .95kg or 1.00kg racetech or sonic springs, set static sag around 1/2 inch,and install the forks flush with the top of the upper triple clamp.Most come with 3 position rebound dampening with the selector on top of the fork.This would give you at least 2 inches of lift,adjustable rebound,the ability to run most any Suzuki dirt bike wheel in 17 to 21 inch sizes,and gives you dual brakes that will haul a GS from sub light speed to stop in negative 2.3 seconds.Just kidding, but they stop really good.Did I mention that the Katana front end is about the same weight or maybe a little lighter.The SV650 shock installed straight up without redrilling the hole gives approx. 3 inches of lift.Depending on how you set the preload and how much loaded weight,it will sag from 1/2 inch to 2 inches.I am running 95 Katana 750 front end and rear shock on my GS.The forks are slid up in the triples about 1.25 inches and my CBR F2 clip ons are top mounted.My bike sits about 2 inches higher than stock with the rear shock preload maxed out(I'm fat) and my static sag in the forks set at about 1 inch.I could raise my bike 2.25 inches in the front and under mount my clip ons,but then they would hit my tank.Dgyver(GStwins member) and I did the Katana front end conversion together.We pressed in the GS stem into the Katana triple and welded it up.I run GS head bearings and everthing else is set up like the Katana.I have a lot of write ups on GS Twins and I have a blog about my black bike.When I finish up my "Lite Tourer" project I will start putting it on my blog.
This is my bike.It is roughly 2 inches taller than a stock GS.I could go up 2.25 inches more in the front by simply adjusting my static sag through longer spacers and lowering the forks in the triple clamps.I would gain probably 1.5 to 2 inches in the rear by installing a stock SV650 shock.Even more if I went with the longer DR650 swing arm.
Just some food for thought.
I should say that IMHO, this set up would give the performance something akin to a V/wee strom or Versys,and be good for gravel running or double track.Your set up will be good at single tack hands down.There is more travel in those forks than the Katana can provided.Maybe more lift if set up with minimum sag.