I have attached a photo of the basic cage. It was going to go into a rally car, but we decided to keep the 75 as a nice road car.
It is the main hoop with back stays, the two front legs and the brace across the top of the front stays at the top of the windscreen.
It is made from 45mm dia seemless carbon steel, which is FIA and MSA spec for motorsport so you'd have no trouble with any regs.
Are you going to race it, track day it, or a road car? If you were going to use it in motorsport it would need a diagonal in the rear stays and door bars, which I'm sure I can sort. If for track use, up to you. The thing with a weld in cage, is that you can add to it. If you want more braces, or triangulation, you can add to it. I've attached a photo of the cage i have in my rally 75, which is based on this cage.
As it stands, I'd take £140 for it or if you want more added to it I can look into this. I can also see if the guy that made it would have time to fit it if you are interested.