I contacted MTH today and they provided the following response:
"The ALP-46 does indeed require O-72 curves for its operation, due in large part to the skirting that hangs down from the body. While the locomotive's length shouldn't be an issue for a tighter curve, the skirting prevents the trucks from rotating far enough to the left or right to negotiate a curve smaller than O-72."
They didnt take a long time to respond to my question. I figured it would take 3-4 days.
Okay, so that narrows down my locomotive choices. Maybe I'll get a LionChief GP40 and have one of the skilled painters here on OGR do it for me.