as far as sanding if I did it I would put the sandpaper on a pane of glass then lightly move the upside down piston in a figure 8 pattern being careful to keep it held square to the work (wet the SP with solvent). I would confirm measurements then order Cometics that would give me .040 at the very very max for the widest one & no less than .030 on the on the tightest one (sand as needed). #1 #1 precision measuring. Holler how it turns out. EDIT use some very very fine grit paper