There isn't much out there for FZ600 stuff. The few years they were raced at the top level it was mostly in production classes. Nobody much made any performance parts. My latest racebike build is running a stock motor and I am spending my time and efforts on upgrading the suspension and wheels. I have first gen SV650 forks and wheels and a CBR rear shock. So far it has been bolt up with a few spacers I have had to make to get it all to fit. I may go with a pair of FJ600 exhaust cams and carbs if I can find them. Here is how mine currently sits. I am setting it up to be legal for V5 and AHRMA Next Gen SBK lightweight.
I agree there is probably not much out there. The FZ600 only had a short production run here in the US... Maybe try the Jap Ebay??? Since I think our 600 was based off their 400 unit back in the day.
Fit the biggest oil radiator you can find. Back in the day my stock motor (with stock rad) would fade noticeably after a couple laps.
This one has a bigger oil cooler,I hoped maybe cams,etc,but it looks like it was preventative,just like you describe.
I seem to remember that bike being nothing but problems for Kurt to the point he regretted ever getting it.