"TomR" writes:

I am not surprised that the dimensions are not the standard that are used
today. It is a very old house with wood lath and plaster walls, old-style
locks on the doors (including skeleton key locks on all of the interior
doors), and none of the interior or exterior doors are standard 80-inch or
even 78-inch door sizes.

Technically, they're known as "ward locks". A skeleton key is a warded
key where the wards have been ground off to make the key universal.

scott