For the CB550 only the 77-78 K models had PD carbs. The PD letters are cast into the carb bodies. There are no accelerator pumps on the Cb550s.
Earlier carbs have the leaf spring main jet retainers. The 74 Cb550K0 should have earlier style 022a carbs, which are stamped on each carb body mount flange, top right.
Cheers,