Arnold - Sunset makes absolutely fabulous models, however being all scale currently O 31 curves are tight for likely all of their recent offerings. I will say that the locomotives can go around tighter radii than advertised, however they have not been guaranteed to work. Good examples in 2 Rail are locomotives from a K4 down will negotiate a 48" radius (096). The 3 rail equivalent might work on an O54 but should be tested. The SP switcher mentioned will likely take a tighter radius than O54.
I might be worth seeing if anyone on this forum who has one has tested it on tighter curves. While I don't have that particular locomotive, it is an excellent little switcher.