I agree with everything that's been posted so far.
Although it uses the same body as a 2046 Hudson, I'm pretty sure a 2-8-4 Berkshire (726, 736, etc.) won't work. The rigid wheelbase is actually longer than a 773! You'll need at least O31 for that.
About the only articulateds, Big Boys, etc., that will work are the K-Line semi-scale ones (which are really S scale 1:64 with their wheels gauged to 1.25" for O gauge track.)
I would read Brianel K-LineGuy's post thoroughly. It's not what will run, it's what looks good. A 2046 will definitely run on O27, but a 2055 looks better. O27 proportioned locos can look pretty convincing with small postwar rolling stock and Plasticville buildings. My $.02.