The C3AE-6090-C’s might be the most misidentified FE heads, due to old books & casting number lists that labeled them as 406 3-2V heads. That’s a possibility, but the majority are just garden variety 1963 model year FE heads.
Our member Ben H. recently posted a few pictures of actual C3AE-C 406 heads, and some identifying info on Facebook, I don’t necessarily want to steal his pictures, hopefully he see’s this thread and will post the pictures here too. I have a set of the garden variety C3AE-C heads, and I added a pic of mine in the valve spring seat area to his on Facebook for comparison.