63-66 sending units vs 67 and up

Anyone know what the differences are between the 63-66 sending unit vs the 67 and up?

Year one lists separate units but there is a guy on ebay selling one unit for all years. I'm not sure what the differences are and I'm wary of ordering the unit on ebay only to find it won't fit the 66.

It's more than half price on ebay vs YO though so it'd be nice if that unit would work.

Thanks guys.