1971 198 slant 6 manifolds

OK, I measured the three bolts on a 83 slant six. The two on the outboard side are actually 4 1/2 inches long. The one in the 'center' is slightly shorter (I didn't take it out) but a longer one would work as it just goes inside the exhaust manifold. The outer ones are definitely 5/16-18 bolts. If you aren't sure of the size, just check the exhaust manifold as they