let us know what you find out. I have stock zx engine in a 72 on su carbs. so same boat. I too have a n42 with a .480 cam.
Wouldn't the thick head gasket negate the added benefit of the n42?
Like Leon says you will need springs, retainers possibly lash pads. Number your rockers, lash pads, springs etc. you may want to use that old cam sometime .