I thought the pitman arm could really only go on one way? On my '50 the shaft has 3 splines that are wider than all the others, and I have to align the arm with those to get it on.
If the '54 gearbox is the same as the '50 gearbox, there are no internal stops- so be careful not to turn it to full stop with any force with the steering linkage disconnected- the manual says that you can damage some things in the gearbox.
I'm using the online manual right now to tear down and inspect 2 gearboxes... it's not as daunting to open them up as I thought it would be.