Here are some brochure scans of two Crayford catalogues I obtained in the early days of ownership and there is the comprehensive website of the Crayford Convertilbe Car Club which will shed some light on their work.
This Brochure is more about the company and what they have made. Judging by their latest conversion a Mk4 Ford Cortina and the Mk1 Vauxhall Cavalier/Opel equivalent I’d say this was around 1977.