Martin... I may be wrong, but picture 4 shows a couple of indents more associated with a front fender ( mudguard ), to clear the fork legs rather than to clear rear frame members, so thinking this actually started life as a front mudguard. Anyone else know if early A7 rear guard has these indents?
The rear section was originally designed to be hinged, yours looks to be a bolt on homespun adaption. The lower edge usually flares out at the bottom. The number plate mount for the year is an open type, rather than the post '53 boxed in type that you have there. Rear light is also a later type, more suited to the later boxed type with an indent to the pressing to make the lens lie more in line with the top of the box.
So, first decide if you can source a better mudguard, one correct for the year. Otherwise making yours fit is not impossible, but will be a real test. To be honest it isn't far off, bolting the guard to the stays will improve things. Aim for the guard to follow the wheel and tyre when off the stand.
The upright arm of the rear mudguard stays are moved slightly forward of true vertical, and bolt inside the mudguard. The rearward arms end up horizontal or more often pointing very slightly down at the rear. Behind the gearbox are two horizontal steel strip mounting stays.
This leaves the awkward to describe arrangement adjacent to the seat spring lower mount. Here the bolt through the frame passes through a cylindrical spacer and supports a bridge piece under the mudguard. The bridge has rivets to mount the guard. The spacers fit into cutouts in the side of the mudguard blade, the bolts do not attach directly to the mudguard blade. See how this compares with what you have.
Lots of pictures available, and maybe some helpful Forum Members can post some as well.
Swarfy.
