This is my take on it. In nearly 60 years the pintle could have been removed, replaced, broken, ,replaced. Depending on where the parts supply was and how often it turned over it is not unlikely whom ever, took what ever pintle was on the shelf, parts bin, or junker out back to replace the pintle an...

The picture posted by Sal represents the type on my 1954. The picture posted by you represents the 1951 outer half of the swivel which has a duplicate rectangular casting to match the rectangular portion of your pintle, and the pintle and swivel are bolted together.. I can not post picts as the site...

Yes the 1954 has the one piece swivel stud as Sal's
The 1951 has the split bolt together version as MilSurp

At first I guess I missed what you are looking for in build dates.
I also have a 1-27-54 with a swiveling pintel.

12-20-51 delivery date WOW/Ord Dept. Swiveling pintle. No evidence of different holes.

Gnome who???

I used the Hingsingm37 method with a sawsall and did not go that bad. The rims were hopelessly rusted to the bead with tires from 1958. One of them did not have a flap. (?) Had to be careful around the rim when cutting the bead but.

Both of mine were Fire Deparment. 1951, 1954.