Just working now on putting a set of 68 to 70 340 manifolds on the EQ Magnum heads. There is a mismatch on the ports that have to be corrected. Not only are the center ports wider but the lower portion port on the exhaust will not seal on the exhaust flange on the heads. Time to make up some flange adapters or do some welding on the exhaust manifold.
I've never tried to install 340/magnum manifolds on EQ heads but an adapter should work if it doesn't push the manifold too far out away from the engine causing interference????