Trying to ascertain your minimum radius for these, you could always look for the original AHM snap track which is based on European Track standards (and has a slightly higher rail height AIR due to the plastic base than other RTR track code 148 like Atlas-Roco, Duddy or PRC Atlas) that came with these sets/locomotives, I believe you're looking at something like O72 radius, not sure but guessing 36"? Too optimistic..tighter? Anyone else here that can weigh in on that Rivarossi sectional track? I'm using all old Roco 1:48 flex and Old Pullman.
The saving grace with them certainly being they can cut sharp (almost traction-like) curves well, very short wheelbase, I think the four axle main driver/frame is something around 4 1/2" and 4 1/4" between the centers of the outer drivers. Note I've added about 1/8" to each side in the above shot.
Definitely a nice kit though, I passed on the IHB scheme and went with a fictional subsidiary of the NYC for my own pike.
The tender on these are GREAT too and likewise have been picked up by kit-bashers too, similarly as the boilers were.
Ah.. the cheap and malleable magic of injection molded styrene. I like the Red Caboose GP kits for the same reason.
Seriously though, based on your plan I think you have enough space to get the kind switching pike you want for these AHM U3a's , certainly diesels like AN NW2's, Atlas SW9's, RC GP's or some of the more rarified small Yoder, MTH or Carworks models. Looks like a great project.
