Best Of

60,000 undersized and 72,000 undersized, is exactly the same thing, IMO. Especially for a system that size.

Is this 1 pipe?

The radiator not heating is likely some problem other than being undersized. You are only consuming that much steam if every radiator is heated fully and that rarely happens. I would go with either boiler and make sure I have all the near boiler piping correct, drips at the boiler if it is counterflow, mains individually connected to the header rather than teed together at the ceiling, using both boiler outlets if available, possibly using a drop header. Insulating the steam piping.

You have close to 0 pickup factor at 282k btu/hr but there is also some measurement error in everything.

Utica uses side outlets, and some do not like it for that reason. But if piped right and skimmed (like any other boiler) they work.