Hi Willy -
I recall a discussion of cast manifolds by GeorgeP a couple years ago that described performance characteristics of them, but I was unable to locate it. I’ll keep looking.
https://pantera.infopop.cc/top...rb-spacer-question-1
In the post above George says there are no carb spacers that can effectively adapt square bore carbs (like Holleys) to the stock (spread bore) manifolds.
Rocky