Heads allowed in modified stock

[novanicks]

I am looking into running SS, specifically SS/AS, or SS/BS. And I cannot seem to understand what heads are permitted. Here is my specific issues:

The rule book says "all heads must be NHRA-accepted". Then also says "aftermarket aluminum cylinder heads permitted except in CS".

Now, I realize there is an NHRA accepted head list, here: https://www.nhraracer.com/Files/Tech...edProducts.pdf

And I realize this discussion has been extensively discussed here:
http://classracer.com/classforum/sho...t=72138&page=2

However, what I do not understand is what provision allows SB2 heads to be used in these classes? They are not on the NHRA approved list and yet I know they are commonly used. Thanks in advance for any help.