I just recently sold my 1957 4" pre-27.
It was a special order from H. H. Harris Co in Chicago Il.
There's a thread on them and I think there were only about 25 of them produced
but I have never seem an actual number as to how many there were.
The 4" was made in 27-2 as standard bbl length, after the Hwy patrol model 28 was dropped mid 70's. You get two less screws and a whole lot of change back.
I completely forgot about it until this thread popped up, I promise I’ll get to it!
That being said I believe it falls between known guns shipped to H.H. Harris of Chicago and it was bought in a gun shop 15 miles west of Chicago so I have a pretty good idea where it was shipped to!