Harold personally I would replace all the steam vents and install the largest sized orifice vents at the furthest point.
The ones located the most distance from the boiler get the air out about the same time the much smaller air vents relieve from the lower floors.
Another viable option I found is FANTASTIC is the use of non electric zone valves which also help fine tune each system for comfort and fuel savings.
As we both know these non electric valves are IDEAL for hydronics applications BUT it will give satisfactory service on vapor systems also.
With great companies like Maid O mist, Hoffman, DanFoss,ETC there are lots of games that can be played to get the most comfort out of even the oldest systems.
Just as long as it isn’t that under slab crap fine tuning is never a problem