As Chris said, take 2 shims out behind the flywheel, it will help move the whole assembly further back. Then if required put washers on the engine shaft to stop the clutchbell moving forward between the front clutchbell bearing and the screw which keeps the clutchbell on the shaft.
Also make sure the engine mounts are pushed as far back towards the rear of the chassis before tightening them up. I know there is not a massive amount of play but 0.5 of a millimeter will also help with clutchbell & spurgear mesh.
I no longer use a the xray flywheel or clutch bells but when i did that was the set up i was using. I now run a mugen flywheel (pins kept loosening on the xray one
) with RMV vented clutchbells. With that set up i had to tweak the same way as you'll have to to get the perfect mesh.
Darren
thanks