Any idea what this is?

[DPittman]

I acquired some bits and pieces recently and among it was this thing I can't figure out what it's purpose was.

The square holes are 1/4" and as in the one picture where I have the thing vertically it appears the square holes line up. The brass thing has a dovetail groove on the bottom.

 

[DavidR8]

Looks like some kind of shop made indicator mount maybe?

 

[Dabbler]

The square mortise with the thumbscrew makes me think - milling machine vise jaw mount. The rest, however is a mystery to me.