Re: 1850's house with boiler system
We are always gladdened when the homeowner chooses to retain the radiators. Many people with historic houses in my area find it a no-brainer to retain the even heat of old radiators, whether steam or hydronic.
For Air/con many people opt for a multi-zone high-velocity-type system. The first floor ducts are run in the basement, and the upstairs ones in the attic or ceilings, that way no huge vertical chases are required between floors.
On one house we did, the steam boiler required replacement, and finding a contractor for that was not easy; very few firms who are familiar with steam want to bother with residential systems.
Remove not the ancient landmark, which your fathers have set.