[Adger Smith]

Ian,
Not enough info. Need to know year and mod of car you plan to use or claim.
The alum head for some cars can be a stock GM (number specific for make and mod) or the Edelbrock 401 casting. Edelborck head usually carries a weight penalty. The carb number will show in the classification guide. (blueprint specs) You don't have to use the specific carb number any more, but it has to be same make with the venturi and throttle bores that match the legal numbered carb.
Those numbers show up in the guide, too.