I believe most, if not all, use the words "use the heaviest gasoline V8 for Classification purposes". So in, say, a 1995 Camaro, you would use the shipping weight for the LT-1 motored version.
Here are some people you can contact
http://www.ihra.com/ContactUs/,
or you can also send a PM (private message) to Danny Waters Sr on here (ClassRacer).