all the single original style speakers available for vehicle radios are all close enuff to right there won't be any problems - they're about 8 ohms, but 4-12 will work, just hafta find one that fits
just figger if the replacement speaker could be fit into your original mounting setup - the 67 radio I've got just has a usual style speaker that's fit to a bracket on the radio that holds it in the right position to be against the metal grillwork in the dash surface - doesn't show the speaker well, but
like this Bill