I wonder if it is a 47-53 cab and what differences there might be in the wiper set up configuration. The door tag appears to be original and indicates it is a 54.
Pretty easy to tell the difference between a '54 cab and a '47-'53. The '54 would have a single piece windshield, while the earlier trucks would have a split windshield. There's probably a little difference in the cowl with the curved windshield of the '54 cab.
I would give Newport a call and ask them about it. Possibly you have '47-'53 wiper transmission arms, but if they worked with the previous motors, that's unlikely.
[on edit] There's definitely a difference between 47-53 and 54 wiper motors. See the attached snip from the 29-54 Parts manual.
