A couple of years ago I used a company near Salisbury called Formhalls who were very good and did all sorts of engine case and bearing work. The alignboard my case and I was very happy with their work and care and attention. http://www.formhalls.com/ Yesterday evening somebody in my Menshed mentioned another good company who have done good work on his motorbike engine, so I thought I'd pass this on as well. I've not used them, but he was very complimentary about them. https://cmesuk.com/
And for anyone north of the grim north, AGRA Engineering in Dundee are very good. https://www.agra-eng.co.uk/services/classic-and-vintage-engineering
