Anyone know offhand what the interchange is on 50s Dodge hemi valve covers? I now have three of them - one stamped Red Ram in good shape, and a pair of plain ones with Super Red Ram decals in so-so shape (surface rust, one is pitted pretty good). I assumed they all fit each other, and these are all the same size, but someone told me there's a difference. Any idea what's fair market on them? The stamped one I don't care so much, it's a great wall hanger, the other ones I don't really need, and I'm wondering if I got boned on what I paid for them.