Is there a difference in radiator supports between BB and SB Chevelles in '66? Someone at a car show told me this but I have never been able to see the difference.

How about right front fenders? Do they all have a hole on the inside near the front edge of the hood for an air conditioning hose or not?

I don't think its safe to look at numbers from a service parts book because they sometimes supercied to the beefiest part or the one that would work in most applications. I'm looking for what was used in production.

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If the supports are different, it's a new one to me. I've never noticed anything special about either.

The hole(s) you are referring to for the A/C are actually in the inner fender and only the A/C cars have them. The rest have a 'dimple' where the hole would/could be drilled.