Hi Tom,
Certainly, "SS Spars" were the original suppliers of Reedcraft boats. Moores seemed to use Holt.
I've just been to inspect my mast. Up till now I had failed to recognise that it had a plaque like yours. That's because mine is completely unreadable. All that remains are the stamped numbers.
This accounts for why I only have an image of the
blue and gold badge mounted a little higher on the mast on the site. I had not realised the significance of the riveted plaque.
Enlarging your image and playing with the contrast, reveals that the line appears to read "Rushden Northampton". Rushden is a small town in Northamptonshire, about 15 miles east of Northampton itself. I had always wondered where SS Spars were based. Interesting too, as Northamptonshire is in the Midlands, about as far from the sea as you can get.