They predate NAD27, so they're not on that GCS/datum. There was a New England datum, but there are no transformations from it to anything else that I'm aware of. The actual coordinate system of the map is unlikely to be geographic aka latitude/longitude, but they annotated it with a graticule and not with the grid (projected coordinate system) information.
You should probably try to georeference it with physical points like buildings or possibly street intersections, not the lat/lon tics.