What did this come off?
318s did not get 4 bbl. manifolds until the late '70s cop cars, and used the standard 360 4 bbl. mid-rise manifold, not the single plane style shown in the pics; it also had a spreadbore flange so did not require an adapter, as well as the choke well becoming the later style and getting an EGR and offset thermostat housing.
273 4 bbl. (Commando/Charger) was not an open plenum as shown in the OP's pix (yes, it could have been modified, but the dividers do not appear to have been cut out).
318s did not get 4 bbl. manifolds until the late '70s cop cars, and used the standard 360 4 bbl. mid-rise manifold, not the single plane style shown in the pics; it also had a spreadbore flange so did not require an adapter, as well as the choke well becoming the later style and getting an EGR and offset thermostat housing.