Here's the poop on the scoop ! ! Or is it the other way around ?
Seems like there's a lot of " Opinions " out there, and now I'll add mine. If you really want the truth, you may have to dig into reliable sources, you know, . .like the FAA or AOPA or EAA.
Near as I understand, you cannot legally leave the certification plate on an engine that has been altered from stock. ( No electronic ignition / high compression pistons etc. ) because it is no longer certified. But, you may want to hang on to the placard, in case some day you want to have it rebuilt as a certified engine. ( Return to stock ). As to the value, it's anybodys guess. If you can find a buyer who recognizes the value you have in it and if you can assure him it's as reliable as stock, you may get the same bucks for it.