HO guage track is actually 32 inches or so. Howver, the Bachman steamers are models of pretty small prototypes which probably would not see service on a big main line.
It sounds like a lot of kitbashing. But as mentiioned above, it S gauge track is about right, that may make it a much easier to build steamers to this this gauge. You coudl use a lot of existing mechanism and just change cabs and maybe some other details.
