28-B-2 and 28-B-3 on the intakes. The exhausts has no number, only a casting sign "S". Both are easy recognisable with their forked support for the roller. The early cam followers have the roller supported at only one side.

Later cam followers are a bit sculptured, does not have any numbers, and the exh. lifters does not have the knife extension for the valve lifter.

All of those different cam followers are interchangable without problem in all Scout, Motoplane, Jr Scout, 741, and Prince engines (with fitted size pivot shafts of course), but without the knife extensions you need a magneto killer button to stop the engine and I would recommend to avoid the early lifters as they are weaker at the roller support.