They are chromed plastic for sure. Look at the upper right corner. You can see where the chrome has peeled away and exposed the yellow plastic underneath.
Bot my 186D and 336D have plastic emblems. Even the model badges on the sides of the hood are plastic. I just ordered the last of the 186D and 336D hood badges from Japan and they're still made of plastic. Nice looking but plastic none the less.
Just for giggles I checked the hood emblem on the Hinomoto and its the same. Heavily chromed plastic. If anyone ever comes up with a way to mold these legally I know a fellow that can chrome plastic.