I would venture to say about half of whatever the going rate is for new 66, maybe a little more if the rest of the saw is in decent shape. Another factor would be who installed these new parts, a regular saw shop or by someone else who tinkers on saws? If both have a reputation for being good wrenches that would up the value a little.
I myself am a little leery of sellers who sell things with new engine parts installed and advertised as being freshly overhauled unless I know them. Saws aren't that big of a deal, compared to a regular engine, there are alot variables that go into rebuilding anything with an engine, some people are really skilled at it, others not so skilled if you get my drift.
Good luck
Larry