Thanks Andrew. Very interesting. This could be a great way to keep my car "original" and have a fifth gear....
I hunted through my magazine stack and it looks like its ended up in the recycling.
The box is a re-manufacture of the CT Wooler - Hewland 5 speed box. I read on Passionford about it shortly after reading the article in the magazine.
I've not found it again on the internet... its being made by a small engineering firm - I recall the price was £3500 which is pretty pricy considering a decent upgraded Quaife type 9 is around half that.