Thanks to all for your advice. I've tried to find a professional dip stripper here in southern Spain
but perhaps fortuitously, haven't found one. The main excuse I've been given is that noxious chemicals are involved which need all kinds of environmental permits. So thanks "deltaten" for the heads up. Anyway I need to consider too what effect the stripper will have on the chrome plated bronze boss.
So scraping and sanding it is although I'll need a new heat gun as the mica internal insulation
on my old one has disintegrated and blown out of the nozzle!
Boatyarddog, thanks for the Bahco tip. I've ordered one from Amazon along with variously shaped blades. I've used one of their 50mm flat scrapers for years with good results including a complete antifoul removal