GX460 air springs will fit if you modify the lower part of the air spring or make a spacer to adapt them to fit the lower coil seat. I did that for a while on mine. But the air compressor setup is a bit tricky.
Otherwise you'll want the ones inside the coil. That's the common setup. Works well. I'd go firestone over airlift for this application because the bag shape is slightly different and I think it works better, but either one will work okay.
Good Luck.