Since its not an 'original' car , or matching no`s car...just block it off like Q said, if you dont find one , just make a temporary, then when you`re ready for a/c ,buy a Vintage Air, you get heat and a/c , but it fits inside under the dash area, not eating up space in the engine room = you can change all spark plugs easily...
the Vintage air looks like factory from the dash view, uses the current vents.....