A couple of things can get you narrowed down to the '53 model year or later. I can provide pictures if you would like.
The drag link is a non-adjustable type (i.e. no cotter pin and big screw in cap to preload spring) This was carried forward through '55 first series trucks. Also different are the spindles and I believe the steering arm. Most obvious difference is the lack of adjusters on the drag link.
I believe the rest of the frame is the same as those trucks back to 1950 (first year of tube shocks)
I am pretty sure brake line arrangement for '53 is new as well. There is a block attached to the back of the master cylinder with two tubes attached instead of 1 as in previous years.
That should narrow it down to pre '53 or post '53
