[Adger Smith]

Karl,
I read the rules a couple of times and saw what I thought was the answer to your question. Since all classes are presented in the rulebook in an orderly "Building" sequence. The later builds on the first. I was just about to say the Stock and SS aftermarket heads would be allowed because they were allowed in classes before the SS/AM category. That is the way it usually happens, but in this case they are not allowed because one line in the SS/Modified rules projects what heads can be used. The wording says "must be OE head with OE casting number". The answer is NO. I know this is not the answer you were looking for.
To make sure I contacted one of my super secret NHRA Tech mentors and I got this answer to the query. NO. So don't show up with an Edelbrock Head in SS/Modified. Guess that closes the door on anything but a factory part number head.