"EA" Stands for "Experimental Application" and "18743" stands for the test number? That sounds a little creative to me. I worked in the Olds Experimental Assembly Department, in Building 64, where we hand built experimental engines, transmissions, other components, and whole cars from scratch. All experimental parts were stamped with an ‘Index Number’. That’s what to look for - a stamped number. There ought to be records to validate part numbers, maybe at the museum.