I found two of these in a box of T stuff and have no idea what they are. A Ford one piece timer fits perfectly in the outer ring and there is a dimple in the bridge that is held in place by the wing nuts that goes into the indent in a one piece timer for the retaining spring. Could it be a fixture for using a one piece timer in a timing cover for a two piece timer?
I believe it's part of a timer elevator set-up. Basically, looks like a distributor, but with a timer at the top instead of a distributor head.
Maybe a converter to allow you to use a later timer on an earlier car, (as I think you suggested).