I run the IMS 3.2 gal unit on my 2002 KX/500 hybrid.
I was able to clearance sparkplug and pipe side using a blow torch and a series of 18mm - 24mm deep well sockets. I would heat them up with the torch and melt and push the plastic up to deform it. It still is a bit tight fitting, and generally takes some patience on reassemble.
It still fits better and easier than my Acerbis 6.6gal tank on my XR650r...