Is the play in the pistons up/down or side to side in the bores? there is supposed to be some side to side movement to allow for expansion in the piston, and also you will have a small amount in the bearings some in the big end and some in the little end (gudgeon pin) to allow for the oil, the oil takes up the slack and acts as a cushion between the surfaces. Thin oil will get past the rings in time too this is normal, rings act more as a friction seal there not completely air tight same again this allows for a thin coat of oil to form on the bores. If every thing was good before you stripped it down it should be fine now.