Bob,
It seems to me that you won't get much extra for your investment by adding anything to the barrels. Ultimately, what you would be doing is investing your time and transport expenses to get it done and expecting that that investment comes back from the buyer. If you do decide to sleeve, I agree with your point about the buyer wanting to choose his own pistons, or use some he could already have. So, overall, I guess I'm suggesting selling them as is, if you do sell them.
Richard L.