A small diversion about rear lights. Early models have a round lamp and on open style of number plate mounting.
The 525 Rear Light is usually found with the later boxed in number plate mount and the lens shape profile follows the line of the top of the box. The number plate mount is flat, and tilts slightly forward: the top of the boxed in section slopes downwards slightly towards the rear, so in side view the profile of the lens tapers towards the rear, giving a smooth aesthetic profile, a straight line from mudguard across the boxed in section and the top of the lens. Problem here is that the visible area of the rear light is relatively small, as is the reflector area of the lens. The later 564 type has a bigger rearward facing lens, on the same basic mounting profile.
The later 564 type is a more chunky lens shape and requires a number plate mount with a pressed indent to effectively lower the rear of the lens down so the top aligns with the top of the boxed section, as before when viewed from the side. This is the style from around 1955 on S/A models and the last of the Plungers
Look at other bikes with boxed in mounts, you will see lots of 564 rear lights canted up at the rear rather than all nicely in line. Fitting this larger lens light to the early flat plate makes safety sense, but ideally needs to be paired with the correct pressing, with a lamp back sized indent, to restore the beauty of the styling. No rush, its probably something you never noticed and probably a flat mount and 564 lamp came with the bike, fitted long ago as replacement when the correct 525 units were rare.
Draganfly's site is worth a look, there is a section illustrating the various lens and lamp types and model years, but for more detailed stuff, Brightspark Magnetos have a large collection of very useful Lucas Catalogues/part applications available to view online, so you can check model year and equipment fitted.
Big thanks to Brightspark for making this information available.
Swarfy.
