I think here is some missunderstanding. Lapping isn't the solution to make cross scratching and make more traps for oil. Lapping is step to make toooooo tight fitting to normal, withut run in ( xtra stress etc). If piston initialy ground to right fitting, I will never do or sugest lap piston. The oil film specialy castor is that strong, so our fitting will not brake it ( otherwise any engine will bluw up just after it start). So that scratches aren't nessecary, more then that from our theory they are very good trap for brasive which creating during the engine run and it start working as unwanted lapping tool ( it is apply to harin cuts on the top f piston) We never do them.