Example:

The following pics are of exhaust manifold bolts for a survivor 1971 340 engine, never apart. BOTH style bolts you see came on this engine, one I call a "Dogbone" head marking, the other being an "M" head. If you buy AMK replacements which are sold as "Factory correct" by most sellers, all of the bolt head markings will be the same, and they will have an "H" on the heads (some Mopar exhaust manifolds DID have "H" head bolts, just not MY example). So, for the 340 I have, they'd be incorrect, but they are dimensionally correct and would work.