Hi Frank
I do this most every week, sometimes daily, however you have very good advise here about how easy you can destroy a piston/sleeve, and most any compound will imbed into the soft metal, and wear the hard metal, that is what happens in this process 99% of the time. If you insist on doing the lapping, go very slow, and leave the piston fit tight, clean it very very well, then clean the parts again, I found a ScotchBright pad, and stiff brush works well for cleaning, and you may just want to use Comet or AJAX instead of a diamond or lapping compound, fine pumice powder... and do not be surprised if you wind up with a useless P/S . The ones here steering you away from lapping are correct, I have seen so many P/S killed by people doing their own polishing or lapping, you really need a real hone, with different grit stones
Regards
Randy