A very nice side valve cylinder; it has a detachable head but there seems to be no provision to fit a cover over the valve springs. It looks rather high (190mm from skirt to top) but the bore is 79 mm. All of this suggests an early-1930s 16H cylinder to me. In quite good condition, no fins missing.
One set of brand new and unmachined aluminium footboards to fit your flat tank Big Four model.
An empty Sturmey Archer gearbox shell: cover and shell are not a matching pair. -GEARBOX SHELL NOW SOLD-
Please make me an offer; interesting vintage Norton spares will be taken in part-exchange.