Joe Baugher's website here:
http://joebaugher.com/usaf_fighters/p39_14.html
shows that P-39N had the V-1710-85 model of the Allison engine. As Bill has side, it does not seem to be the engine data plate, as it is lacking some of the information (such as valve adjustment specs) normally shown on those plates. Could this have come from gear box on a Russian P-39N?