This is probably old news, but I just stumbled across this Land Rover technical document for the paint that shows what kind of paints were originally used for each color.
http://www.seriesdefender.com/manuals/Land Rover Paint Codes.pdf
It looks like they list single stage urethane as "clearcoat." It says Monza is a base/clear, but I went with a single stage urethane like the original Portofino. It also doesn't list Glasurit as a supplier, but that doesn't matter because it's good paint. I read on another forum someone said it cost less overall than PPG because it's a higher solids paint, even though it's more expensive by volume. I also didn't know some of the colors like Arles were an ALKYD paint instead of a urethane, but it also shows Beluga as a single stage and I thought that was a base/clear.
If I was doing this over again I think I would choose Willow Green because I've become really fond of that and it seems like Land Rovers should be green, but that's also a base/clear. A single stage makes for easier repairs and can be fixed up later, so I don't regret that. I think a metallic single stage would be difficult to work with. I'm not sure how good a non-metallic Willow Green would look. Maybe the correct choice would be Pastel Green.
I used PPG SHOP-Line acrylic enamel. Its a single stage paint