You can select shells with numbers iirc, personaqlly I use mousewheel. Just bind the keys in a way that they don't conflict and you'll be fine.
To check which kind of shell you have selected, you could take a look at the number of shells when you enter the tank. By remembering the number, you can keep track on how far down you are on both types and therefore see which one you have selected. A bit more complicated than an addition to the UI, but I'm not sure if that's possible/planned.
GL tanking!
