Depends what facilities you've got and how much time you have. If you have a large shed in which to dismantle the entire Land Rover and don't have neighbours who will object to the sound of a drill or grinder going for hours on end with a wire brush attachment, it's worth cleaning the whole thing down to bare metal and painting it. If, like many of us, you live in a built up area and don't have anywhere good to work, the advantage of Dinitrol, Waxoyl, etc. is they can be applied to the chassis in situ, sprayed on fairly rapidly and the oily texture means that it's not critical if there's a little dirt about. Having tried to get Dinitrol off some components with a wire brush on an angle grinder so I could paint them, it's clear that it's very clingy, even to rusty surfaces, and hard to get off. Whereas most paints would flake off a less than perfect surface. Just what you want.