1971 198 slant 6 manifolds

You have the manifolds there with you. None of us has them. You are going to have to determine what sizes you have, because they used both 5/16 and 3/8 in that inboard hole. That's why the inboard hole on that gasket in the link up there and all of them like it have the inboard hole 3/8. I personally have never in my life seen one where the inboard hole was 5/16 OR a bolt and I've seen a lot of them. All of them I've ever seen were a stud and a 3/8 coarse thread stud. You've been told multiple times on more than one thread what the deal is. You're going to have to figure out what you have there based on the manifolds you have. We're not going to be able to do that for you.