I've done these 2 that were offered in Hallmark stores years ago.
I don't have a pic handy of my completed ones, but I did get far enough that I tried to use the puzzle glue to hold them together for possible framing. I had a little bit of the glue leak through to the front surface in an area or 2, though in general I think the gluing went well considering I had never done it before. (while I think the glue instructions said you could glue the front surface, I was reluctant to do that, not knowing how it might look if the glue was a bit uneven, or how the glue might change the look of the unaltered surface). If I do some day go through with the framing, I would try to see if there was a safe way to remove some of the excess glue showing through before completing the frame.
The odd sizes of these particular puzzles make finding a simple "off the shelf" poster frame difficult (the shorter dimension is larger than the somewhat standard 2' x 3' sizes you can easily find for movie posters in Target, Walmart, etc).
I had considered a few possibilities using plexiglass, maybe thin hardboard for the back and some method of holding it all together using some sort of molding to allow screwing the assembly together in a way that wouldn't show too badly. I never did push the thought through to completion though.
Here are some box pics snagged from the net:
I fully agree on difficulty of the one you did. Those nearly identical pictures would be really really hard to put together if they were all mixed up in one bag!
The one I showed above with the 5 painted engines was hard with the smoke from the steam engines and the clouds. The PW wall of trains had some challenges too. It's amazing how the stripes of a crossing gate can be mistaken for a small detail on a piece of rolling stock or engine.
Good topic!
-Dave