Shaun,
If your frame is CA7 153, that would make it early 1954.
CA7 frames didn't have the sidecar mount in the rear loop as shown above.
A frame that early would not have any cast front engine mount lugs on the front down tube, only 4 tubular lugs.
All frames except GA7 have the switch mounting plate welded to the loop.
A '58 frame should have an FA7 prefix. The Flash engine number prefix became DA10 for 1958, CA10 before.
Does your rear brake lever on the brake plate point up or down?
Up with the cable adjuster in the casting on FA7, down with the cable adjuster in a fitting on the torque arm anchor point on GA7.
After all this time and probably many disasters, you could have anything.
Trev.