I think it is a late to mid fifties too with what looks like a tag axle as indicated by the radius rod on the suspension. That would make it a factory setup because of the 42,000 GVW rating. A fairly heavy truck by the standards of the day.

1953 Chevy 5-window 3100
In the Stovebolt Gallery
More pix on Picturetrail

Dave
Engine & Driveline Moderator

If you can't make seventy by an easy road, don't go. ~~ Mark Twain