I’ve been melting pavement with a variety of FEs for 20+ years and professionally building them for almost as long. In those years I've came across alot of strange casting and part #s in the FEs. A couple of years ago I ran across a set of heads from a 352 in an old Police car from New Mexico, C5AE-275-2143-C I was completely baffled !!! I called a friend of mine up in Dearborn (Ford exec. In New Product Development) He called me back and said "Nice one, you had me going for awhile! Next time your joking around with me, Give me a real Head # instead of a Distributor Part Number" It took me a half hour and a some pics with my Digital camera to convince him they where really on the heads. Your heads my be part of the same mix up, Check the #s again and see if you missed any.