Pistons/reconditioning

As for the moly coatings, I would be concerned about the bond with the piston. If these have been run for a while, plenty of oil is baked into the pores of the aluminum, possibly interfering with the adhesion of a coating. You could try it, but I doubt you will notice any difference in performance.

As for the phosphoric acid wash, again it would probably be a waste of time. But then again, if you were going to alodine the pistons...

When I re-use pistons, or other small engine parts, I typically dunk them, make sure the ring lands are free of carbon, and run them through the dishwasher (send wife out shopping).