2503D must be new, I don't recall that one.

IIRC, A was for low altitude tacair, B was for artillery (and maybe air too), C was for high alt tacair.

A and B were used for routine marine training ops, C was used rarely (marine pilots are supposed to be down in the mud with the troops, not doing ACM up high.

But yeah, check with LR. I'd be more worried about B...arty rounds can't see and avoid.