AN = 37° seat with fittings usually made from aluminum with standard NF threads
JIC = 37° seat with fittings usually made from steel with standard NF threads
for most things, they are completely interchangeable.
the hoses at the start station of the locomotive [gm/emd i am assuming] are either dayco, gates or eaton/aeroquip depending on who made them. the original emd stuff seems to be mostly aeroquip [blue covering] the equal in dayco is black covering. the gates equal is in a green covering. those are the standard colors they come in for those brands, but other colors are avalable too. .
i know at the diesel shop where i use to work [on the locomotives] we use to stock the aeroquip hose, but then started stocking the gates stuff. same quality, different price [when you buy in spools, a little price change per foot makes a big deal]
the gates stuff we stock is C5D hose along with their field serviceable fittings in jic and npt for the hose in -6 to -12. we do have some larger stuff sometimes for the ge diesel engines [-24 or -32]
the fittings between the field serviceable hoses from brand to brand seem to interchange well from one brands hose to other brands fitting.
they are a little different though. the field serviceable hose is smaller in the ID than the -dash would indicate. a -8 field serviceable hose is 13/32" id iirc