Cylinder head mismatch

Good day!

New to the group, thought I would post a question or two. I have no real BBC experience, I have always built SBC's, but I am building a BBC for my 55 Chev and taking the car off the track and putting it on the street. The bottom end is done, but the heads I purchased were supposed to be a set of #3917215's. One head is, but the other is a #3964290. The guy I bought them from insures me they are the same casting just different numbers. I would like to know if anyone knows if there is a difference between the two.