Get this kit, never have shimming problem again.
http://www.amain.com/OFNA-1-8-Clutch...Shim-Kit/p2940

The two black stepped washers with the desired std shims are a perfect remedy for the problem you have.

Also whats the gap behind the flywheel, should always keep it to a minimum, about 1-1.5mm

Or use a countersink screw.

How much back and forth play should the clutchbell have ?

I learnt that anywhere between .3mm and 1mm will do fine. TKO recommend between .3mm and .7mm for their Special Clutch bearings.