Deerfield was built out almost entirely after the Second World War, mostly between 1955 and 1975, and the split-level is its signature building. Colonials and ranches fill in around it, and since the 1990s there has been steady teardown-and-rebuild activity on the older streets.
That makes it an easier town to work in than anything on the pre-war North Shore. Supply is copper, the waste is cast iron or early plastic and usually sound, the framing is dimensional and predictable, and the bathrooms were built at a size that still works: seven or eight feet square rather than five by seven.
So the work here is not rescue, it is planning. A double vanity and a walk-in shower almost always fit without structural work. What actually needs solving is where the waste run goes in a split-level — the floors are staggered, so a drain has fewer places to go than the plan suggests — and getting the extraction properly ducted, which in these houses is very often not the case.