Trafalgar Yacht Services specialise in Westerly spares and the folk there have a deep knowledge of who made what ( a tough task bearing in mind the number of suppliers involved as the company jumped in and out of solvency).
I just wanted to welcome another Griffon owner to the forums.
I don't have an answer for you question, as I have decided tour forehatch can last at least another season or so. What's up with yours? Our has crazed perpex, and part of the hinge is damaged, but I fixed the leak (fingers crossed) last winter.
I too have a Mk1 Griffon where the forehatch is leaking and needs replacing/resealing. Trafalgar Yacht Services do have suitable replacements ( My original was made by Campa) but I believe that there may be problems in removing the hatch as Westerly glassed over the nuts on the fastening bolts under the deckhead. Advice from anyone who has actually done this job would be great!