The journal box covers on the trucks under tank 28 have plywood covers too. I'll take a closer look when I visit the rolling stock parked north of Carcross later this spring to see if this is the case with the other ESTADO trucks. My guess on the lug was also for retaining chains.
An oft repeated WP&Y rumour is that the USA 'metric' boxcars and flatcars were destined for Brazil before the Army sidetracked them to Alaska. The ESTADO trucks probably came from those cars. Of course Brazil is Portuguese not Spanish so it's just another unfounded rumour probably as incorrect as the 190s being diverted from "Iran".
Mike