The problem is the pre 72 manifolds used 5/16-18 bolts in all three positions. Chrysler changed the inboard hole to a 3/8-16 stud in 1973. The older exhaust manifold inboard bolt commonly broke off on replacing the exhaust manifold,so Chrysler resolved this by using a 3/8 stud. All you have to do is drill that hole in the intake manifold to fit the 3/8 stud. The stud is 3 5/8 inches long and is 3/8-16 thread. Slantsixdan has written about this solution in the past.
