I don't think the "...reinforced ribs are just that...".
I think they are replacement ribs. I think they removed the originals, and riveted the bigger better ones on, using mostly the same holes.
Note that the thickness of the sheet metal for the stamped rib is 3-4 times thicker than that of the adjacent rib. And, of course, there's the addition of the bar stock over the new stamping. I wonder if that happened when the replacement rib(s) was installed, or later.
Unless some kind soul offers these replacement ribs, I believe my modeling approach will be to assume the new ribs were added sometime after the cars were put into container service. Though it would be Way-Kuul to model the car I photographed. It also shows up in Thompson's book, so it's very popular.
The big-ribs weren't just added to the container gons. One of the photos is of GN 72641--not in the special series.
When the big-ribs were added is kinda up in the air. So I'll likely paint mine in "regular" GN (instead of the Big Sky black scheme) and run them in 1960.
And, yes, it would be great if the Sunshine kits "reappeared". The prototype for the model was owned by GN, NP and SP&S.