Exhaust Leak

We didn't have any bolts (technically "capscrews") or studs broken off. I think what actually happened on ours was that the thin stamped steel gaskets rusted through. Probably because they were scraping back and forth with expansion and contraction of the heads and manifolds. Then once it started to leak it leaked more, ate up more gasket, exposed the manifold to warping. That said, the 460 (and the 454 Chevy) both do it. The fact that it's in a van "nose" adds to the problem because heat is trapped. My repair was manifold work as described above, followed by replacing the 2-1/2" exhaust system with a full flow 3" system. That difference is not simply "half an inch" because it's a Pi*R-square" calculation. The larger diameter plus a better muffler and mandrel bent tubing (no wrinkles in bends) made a huge difference in power. Again, not so much in mileage. It also helped the engine run cooler. Had no further trouble with manifold leaks. So the original Manifolds and Crossover Pipe stayed in play. The 1983 was not equipped with a Catalytic Converter. The 3" exhaust system was a "cat back" system that I extended forward to where the cat normally is.
EDIT to add: My plan for if/when manifolds cracked or could not be re-surfaced, was Thorley Headers. They have a connector pipe available. I think it came with the set.