Now, I'm not a diesel mechanic, nor am I going to start pretending to be one, and I by no means know what the inner workings, adjustment nuts on a 244 fuel pump are like...
However, let me ask this question. Are sockets not the same as wrench heads? Would a ratchet and socket setup work in this situation?
ATK mentions that wrenches are too thick to fit into the window, so I'm not sure if your clearance problem is due to the space between the bolt and a "wall" down a "shaft," or if it's a matter of there not being enough space for a wrench to sit square on the bolt and be able to torque the wrench to make your adjustment.
Another trick, if you don't mind buying a new wrench, is something I saw on "American Hot Rod." One of the mechanics in the shop couldn't get the wrench to fit in the tight space between the engine and wheel well of a '65 mustang, so he went to the workbench, and gripped the open end in a vice. He then took an Oxy-Acetaline torch and heated the "neck" closest to the head and bent the wrench to fit the angle of the bolt in the engine compartment. If you want to do that, just remember to watch your heat, so you don't undo the temper of the steel.
Just thinking you could "modify" a tool to better fit the situation, if a "specialty" tool for said adjustment doesn't already exist. (At least, if you made one, then you'd have it around for future adjustments!)
So, Paul, I don't know if I helped you by "thinking outside the box," or if I've just been an annoyance. Like I said, I have no clue what a fuel pump on a 244 (or any locomotive for that matter) looks like. Just wish we were sitting at a bar with a pen and a piece of paper...
Anyway, good luck on the adjustments, and sorry if I've been more of a hinderance than a help.