In theory, you could do each axle individually. If all 4 axles are quartered, then they should work together just fine.
When pressing them on the axle, you need to do it carefully so they remain quartered. Micromark sells a tool/jig for quartering HO scale drivers, but I don't think they have one for O Size drivers.
I don't know what kind of mech this loco has. If all the axles are geared like old Lionel, then the quartering can be pretty loose since the gears transfer power, and you can set the side rods loose enough to make up for errors.
If the loco has a single gearbox on one axle, and then the side rods transfer power to the other axles the quartering has to be pretty accurate.
There is a custom builder in Calif that took over the Jerry White business, that might do this for you. I can't find his name now, but I will continue looking.
