Never took it any further Robotsan but Geoff who's doing a stunnning job on a white 260Z used invictaspraychrome.co.uk on his and was very pleased. It was one of those jobs for this winter that got took over by life ! .........Hope this helps
Damn, unfortunately he has retired now!
I've spoken to so many companies now, and aside from chromespray.com, the only true metallising company that will do the job is https://www.morganicmetalsolutions.com/. Spoke to a lovely chap there called Will who explained the process in full. You get a nice weighty piece of plastic back with a true chrome layer on top. Which does sound cool, but the downside is A) I have to remove the existing finish myself and get the plastic really smooth first, and B) they have a minimum order of £350 - but that is plus chroming which is done by another company. He's getting back to me with the price for that. Oh and it will also add 0.5mm to the whole thing, so that could possibly cause a problem with fitting.
The upside is, he reckons I could get other parts chromed for that minimum price too, so I'm considering getting the dash vents done too.
But on the other hand, chromespray.com only costs £120 for both sides, and their finishes do look really good, as long as the item is prepped well.