i live in texas, and don't ask me why, but all the houses around here have gas furnaces. really, it makes no sense considering i grew up in PA where we had a heat pump. go figure.
in any case, i have two units in the attic and both had old horizontal A coils to start with, however i'm replacing the smaller one with a horizontal N coil and the other one already had an N coil put in it a couple years ago. the system works better than it ever had before, that's for sure. blows a ton colder just with the new coil.
Just do it, you might save a couple thousand bucks