That would have been nice for us hot-rodders here 20 years later but even before the Magnum came out the only vehicles getting V-8s were trucks and SUVs. Not much benefit to having a big-port head on an engine that will rarely see over 4000 RPM and needs stump-pulling torque for doing truck things.
Yeah the 5.7L Hemi is put in trucks and they have giant head ports but those engines don't pull down low like a 5.9L Magnum does.