Thanks for that. My guess is also it was a retro fit. It's from Holt Allen. Operation seems pretty straightforward - I have a Jib and Genoa, although I've not tried to rig either yet.
The sail number (206) has helped date it a bit, as has the badge on the original and replacement sails (I have both sets). The original set (all there but tatty) has the Jeckells tear drop label from 1970, the sail bag has an older looking style but same slogan. So pre 1976. (Pictured)

The replacement set has a 1989-1994 logo.
On the subject of rigging I had a good read of the set you posted - I can't visualise the end of the boom set and how it's routed to the cleats. I'm not what I have is correct. Also, I'm missing the kicking strap.
This is what I have at the moment.

Anyway, great website and thanks for the advice.
Simon