Hi Rob, If you keep me in mind for the next rad cap tool that comes past you. I will allow you to do whatever you wanted to do in the first place.
(it's such a small commitment)
Each one would need a gasket or gaskets of various thicknesses to have the over flow tube to point in a suitable direction, when it tightens down.
This system negates all the b.s. (british standard) associated with checking the water level in an original carrier set up.
buy a suitable ebay neck to suit a 4 pound cap that is available in your area. the caps come in two heights. Be careful selecting. The original cap is set to about 3.5 pounds. The radiator should cope wit 4 pounds. I wouldn't go any higher with original tanks.
Go for it.
Jim, Talk to Rob. He might be the North American distributor??????????