Hello Solo! I recognise you from Advent...welcome. I forgot about this thread and therefor haven't updated my endevours. Too bad, you may not like what i have to say:
I found the 4054's to be unsuitable for the GS100. They are too small and light, mainly fecause the trippleclamp on the GS has a much shorter pin. Also, the 4054 has a very small 12mm axel. Basically, the fork would not be much better than the stock in the end. I ended up buying a set set of 4860's from E-Bay for $400.
This is where things get tricky. You will need a trippleclamp to go with it. You can use a KTM trippleclamp which will alter the geometry of the bike, but only slightly. This affords you the option of using a KTM front wheel (Accel) and KTM brakes. I actually built my own trippleclamp, milled from billet aluminum, and had a 210-21 wheel built by Woody's Wheelworks with the heavy spokes and a Rad Eagle billet hub, and then machined up the required spacers. The major problem i had with a stock KTM trippleclamp was the off-set. The stock BMW offset is 26mm, the KTM offset is 18-20mm, depending on the clamp. This tightens up the front end considerably, and i had clearence issues with the PD tank, the clamp hits the tank and reduces your turning radius. I don't know if this is a problem with the stock GS tank. If you decide to go the rout of building a custom trippleclamp, bake sure you copy the KTM fork spacing EXACTLY! I was off by 2mm and this created a huge clearence problem with the brake disk. I had to machine the fork itself, and my wheel is offset by 2mm . Only change the offset to 26mm.
Yoiu need to machine a new pin which holds the bearings for the steering head, there is no stock match to the BMW bearing size. Also, the pin is a specific length and much dhorter than most dirtbikes by about 25mm.
The KTM950 forks are a standard 4860 fork found on ALL their later bikes, only with shorter springs and a 3.5" spacer on the dampening rod. Basicly, the spacer doesnot allow the fork to fully extend back to 11.5". The springs are cut short the same amount. The springs i used are .48kg/mm Raceteck, and are very stiff, good for a heavily loaded travelbike and very agressive. The forks were modified by Holeshot Racing in Langly, ant the mods cost about $400.
Ditch the 4054's and get the 4860's! If your going to go through with this mod, may as well do it right. The current KTM Hardparts are awesome! I use the 310mm Wave rotor and a Berringer 4-pot caliper. I reduced the master cylinder to a 12mm (stock BMW)...the brakes are HUGE!!
You can check out some photo's in the Copper Canyon file at http://homepage.mac.com/adventman/