The truck in the bottom photo is a 50-ton AAR standard solid bearing type from Accurail. Solid bearing trucks were banned from interchange in about 1993, but cars thus equipped started to disappear quite a few years earlier.
The top photo is the old Model Die Casting roller bearing truck. It isn't a particularly good model of a specific prototype, but probably is closest to a Barber 77-ton design. These showed up in quantity by the 1960s, and are still around today.
Rob Spangler
I always forget whatever I knew on these details. Looks to me like the top photo shows a roller bearing truck, the one in the lower photo a bit earlier vintage.
See the history in a related December 2003 MR article that you can download.
https://mrr.trains.com/~/media/import/files/pdf/4/c/c/mr_pi_5-06_freightcartrucks.ashx
Here is a short article from Trains magazine.
https://trn.trains.com/railroads/abcs-of-railroading/2006/05/freight-car-trucks-and-carbodies
Paul
Modeling HO with a transition era UP bent
What is the difference between these trucks. Obviosly ones old and ones new, but when did the switch happen? Would you find both styles on trains?
Thank you!