Buick caused the confusion on the '67 small-block V8 fuel pumps. Sometime during the '67 production run, the factory discontinued the tank return line and 3-line fuel pump on the 340 4bbl with A/C. This resulted in a 1st and 2nd type part number for the pump on these engines. Other 300 and 340 cars with A/C used the return line setup and 3-line pump all year. Many aftermarket part suppliers likely got mixed up following this mid-year change.
See attached page (group 3.900) from the Buick Master Parts Book printed in '72 for more info. In any case only two part numbers were used on the small block V8 and V6 pumps that year. The difference being with or without the return line pipe.