The principal specialists are Fourways, followed by Z Farm in Thirsk, North Yorkshire. Andy Plant, who makes an extensive range of repair and RHD swap panels as the APS brand, is based out of the Z Farm, working with its proprietor Duncan Pearcey.
If I was recommending a third party for fabrication like a RHD swap in the NW, I’d say TLJ Welding in Macc. They would not be cheap, but I’ve used them for a few bits and they are highly competent. Last time I went in, they had a Testarossa shell in for a full rust repair session. I only recognised what it was from the profile of the rear panel- much of the rest was devoid of exterior panels!
Ultimately, it’s about knowing and trusting fabricators and body shops/garages that can handle whatever you have. Trevor Farrington is another well known resto business in Cheshire. Recommended and charging Cheshire prices as one could expect! For general garage stuff, servicing, etc., longtime Zedder and friend Mark Warburton here in Macc is a good, economical bet. He’s been around Zs since the 80s/90s, and is where I go to do any work on my cars that need a lift! Zs aren’t hard to work on though, so any competent, trustworthy mechanic should be able to handle the basic stuff.
Of course, I could do a lot of the above stuff - but not until I sack my day job off in a few years time and turn the hobby professional!
Let me guess, Kameari make a really nice one?