I have no idea what prototype these old Arnold trucks might be based on, but some have noted that they bear at least a passing resemblance to European "swan neck" trucks (aka Schwanenhals-Drehgestelle / Pennsylvania-Bogies) -
In any case, they look like they'd be quite at home under an 1890-1910 era passenger car or caboose. The raised edges around the sideframes likely make them cast-steel (as opposed to wood beam), but beyond that it's anybody's guess what they really are.
Mainly associated with their "old-time" passenger cars, Arnold also used these trucks under their shorty streamliner models (the mind reels) -
