Thanks for the replies and information.
Yes, the B&O had 58" drivers on its first S-1 2-10-2 locos, and went to 64" on the later S-1a locos. Those seem to be about 1" larger than the USRA light and heavy designs. I do have driver spacing info for both the USRA heavy and the B&O S-1a, and they are the same at 67". So, I guess the B&O just had 1" less clearance between driver flanges.
Anyway, that is good news for getting a frame and drive wheels for an N scale model.
Trying to mike the Con-Cor "Rail Baron" USRA Heavy model, the wheels seem to be about 61.5"and the flanges seem to be about 70", with the spacing at about 72". So, as Spookshow Mark pointed out, there are some minor variations from the prototype dimensions, particularly the wheelbase being a tad long, but is seems to "look right" so far as N scale is concerned.
Anybody planning to make a 3-D print for this model to convert to a B&O S1a?