[Arran]

Don't use muriatic acid, it will take the rust off but it will also make it rust again. What I would do is try electrolysis to strip the old rust and paint off, basically you need a battery charger or DC power supply, a piece of scrap metal, baking or washing soda, and a bucket of water, there are several good how to videos on your tube. Another method if you want to try preserving some of the original paint is soaking the cabinet in a 6:1 mix of molasses and water for about a week or two. It looks to me like the original paint was some sort of crackle finish, I don't even know if you can buy it anymore but there used to be a few recipes on how to make it.
Regards
Arran