This Maerklin/Trix UP box car was bought for one reason only, it has Alternate Center Rivets, and apart from resin kits I believe this is the only plastic model of a car with this arrangement? Anyway this is a B-50-24/27 a 1937 AAR variant, which due to the steel used required an extra line of rivets between the panels. In other words a true rivet counters delight.
Mike Brock, owner of the Steam Era Freight Car list, and all round UP guru has given the models a qualified thumbs up. Main issues are the trucks and couplers. It also needs coupler cut levers and air hoses. The roof pattern is not quite right, but noted as something that one will need to decide what they want to do?
It would be a lot of effort to cut the roof off and replace it. A non-trivial job, but who am I to speak as I've already turned a perfectly acceptable War Emergency gondola from Tichy into effectively a kit, so we shall see how I feel when the time comes for this car to enter the work bench.
I shall have to find some photographs and come to my own conclusions. I understand that there is an article by Richard Hendrickson on Union Pacific B-50-24 and B-50-27 Class Steel Box Cars using the Marklin models, in The Streamliner. Vol. 17 No. 1 (Winter 2003), which I shall try to get hold of.
Finally, many thanks to Barry Bennett for pointing me in the right direction for getting hold of one of these cars at a reasonable price. Thank you.