My Christmas present to myself was a GP60 in demonstrator paint via an Athearn blue box kit. Being an older kit it did not come with knuckle couplers. I figured I'd have to figure out which couplers would fit and order them but just on a whim I checked my box of parts and I had just one pair left and they just happened to be the right height (#42's).
Now I just have to figure what decoder to get and finish putting on the detail parts (why are the holes never the right size?).