I think GE of Brazil and Spain (liscencee?) are probably the most ctive in narrow gauge designs. Actually, many of the smaller GE designs allow the gauge to be narrowed, generally the width of the locomotive is the drawback. Most of the 44 ton+ GE's are 9-6 wide, but the standard 70 tonner is 10-0 with full width traction motors. 25 tonners are usually 8-0 wide.
EMD has had a ng traction motor for years, but I have never known the to build a 36" gauge traction motor. Plenty of meter gauge and up. I heard a claim that there have been some smaller EMD type engines converted or built for 36" gauge, but they use an indirect d-e drive - traction motor to a differential like the GA8's (chain to other axle?).
DIFCO built the third set of steel cars for USG in Plaster City (first new bottom dumps to work with the MLW's), but Trinity had evidently bought out DIFCO so they built the last order (slightly different paint color and additional step on the stirrups). USG claims to own the truck patterns which are a bettendorf type but still use outside hung brakeshoes.
Other than USG and WP&Y - is there any ng left in North America other than tourist and mine operations?
Thanks for the BB40T-2 link, those somehow got by me.