Dofasco was a Canadian railcar manufacturer from 1962 to 1994 (possibly associated with National Steel Car of Hamilton, Ontario). There isn't a lot of information out there about them, but evidently they manufactured 70T and 100T freight car trucks (one of which was designated as the type "S-2" truck).
According to Rapido Trains, the trucks used on their GP20 tank cars and some of their centerbeam flat cars represent two different types of 100T Dofasco trucks -
