Just wondering if you have the older 1993~1999 Open Enduro (steel tank) model?
The reason I ask is that the XT600 tank is fitted in much the same way the older Open Enduro models are. The tank does not bolt at the front, instead it has two rubber mounts to hold it in place (see diagram below) and bolts at the rear.
If you do have the older model it may be worth trying it?
Jarrah
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2000 TT-R250M-
Spoiler
Ported & polished, 73mm bore, Wizeco piston, US header pipe, FMF Q4, #150 main jet, #52.5 pilot jet, throttle stop screw adjusted, larger snorkel, GYT-R air filter, NGK Iridium spark plug, 14/51 gearing, NOS +
"The 21 litre Acerbis tank is exactly the same as the one they sell for XRs. A bit Fugly, but practical. Just need to make up some sturdy mount brackets (picture below) for the front. With that on, even with hard riding, you'll get around 400km which is plenty for anything I did (which was mostly multi-day trips with tents etc etc.)"