Thanks for your help and info Chico. When you put it like that it does make more sense as, as I said, I have a latitude already which does exactly that, and does not have an external cup on the bottom. That said, not sure why you’d ever want to turn your forks more than 90 degrees either direction? In an accident I suppose.
The forks are (currently) 1 1/8th, with a good 200mm+ on the steerer. I’ve found plenty of top parts which will fit (probably for taper steerers) but the bottom seems the mess. The most confusing of all is the internal and external diameters. There seems to be no standard, and until you click onto every headset you are browsing, you have no idea what the size is!!