Yes it is an original-you are missing the tank top,tank bowl and the needle valve assembly (the needle and friction spring)-and the jet assembly itself does not look to be in particularly good condition. You would need to locate both those items to get the engine into workable condition-and the tank top (or a washer of identical thickness to the tank top) is required because the jet assembly screws into the intake from below-and the hole through the intake tube passes through the jet assembly-and is drilled AFTER ASSEMBLY-ie after the jet assembly is screwed into the air intake tube-so you cannot just screw the existing jet assembly further in till it bottoms out on the intake-the through hole will then not be aligned...so even if you want to use a Mills 75 with an external tank, you still need the tank top to remain in position. There were two distinct models of the Mills 75 mk2-the S.75 (='standard') which had a rotating cutout between the venturi and the tank, and the more commonly encountered P.75 (='popular') which dispensed with the cutout-for obviously reasons the jet assemblies on the two variants were slightly different.

ChrisM
'ffkiwi'