ID mystery spacer ???

Ford did do a speadbore, on 429 vanilla motors, and probably 400M. Not sure which carb. (Quadrajet?)(Autolite?)
Got a die grinder and a sanding roll? You've got two templates to enlarge it to.
Edit :Ford used a 4350 Motorcraft spreadbore, and also quadrajets. Quadrajet or thermoquad will not fit on a 4350 specific manifold.