Thinking a bit more about your disk, it may well not be a GSXR disk as you have it bolted up using the existing holes?
To fit mine, I had to re-drill mounting holes to fit the RGV wheel.
Also put a 5mm "Top hat" spacer behind the disk to mount it out a little further.
The pics below are for the Gen 1 fork and brake set up.
4mm spacer between fork leg mounting holes and caliper but other than that the caliper bolts straight up with no adapter plate required!
As I said before the disk is now 315mm instead of the original 320mm, but that makes stuff all diff!
My Gen 1 frame and forks are a 97 model (Don't know if they changed in 98 & 99?
The pics below were of the adaptor bracket for the steely and a shit load of work went into milling up that bracket and cost me about $200!
(Don't think that's what you were getting at though?)
You're after the Gen 1 set up, yea?!
Rgv rear caliper mount will be welded in this week and then hopefully start with the bracing of the swing arm next week some time.
We've got a ride day coming up in August it needs to be ready by, so the pressure is on!
The front caliper was from my 04 Yamaha wr450 motard kit which is a 4 piston Braking caliper and I believe that Casons Imports (Sydney?) still had a few on the shelf due to there being some issues with that particular caliper leaking from the centre joint.
When I made some enquiries about getting another for a spare they told me they would sell one to me with no warranty for around the $240 mark.(If I remember correctly?)
I spoke with a Brake company here in South Aus. that had seen this issue with the Braking caliper and he seemed to think he may be able to fix the issue if it occured but I just let it go due to the one I already have working fine and has great feel.
They may still have some? (Getting them to admit it was the hardest thing!)
Will post some more pics when all fitted up properly and tested!