Or, you could use a set of 273/ 318 manifolds to fit your body style. Everything would bolt up and seal. Of course it will choke your exhaust flow down, defeating the increased flow of the magnum heads. I thing the magnum manifold on the drivers side hits the firewall.
That's why I thought that a inexpensive shorty style header would be wanted, better flow than a manifold plus the ground clearance and easier to work on too.
