RE: 91 OS head
The OSSurpass II head will not work for the intake manifold bolts on differently
If all is wrong is that the glow plug or the exhaust is stripped out, there is a guy or two that can fix that?
The Magnum sure looks like a Surpass I, but you are on your own as to whether it will work or not?
I know the valve covers will interchange if that makes you feel any better