Mine ia a different make but it can adjust the cutter/reamer position up and down the shaft using 2 threaded collars like OPs. The silver collar probably goes on the flat side of the face cutter and the black scraped up collar goes inside the headtube below the reamer, which appears to be missing, and holds the reamer facer assy in place. Maybe ?? It is hard to tell with it assembled. I like the BB thread chaser.

If the adjustable reamer won't go quite big enough I have cut brass shim stock and put it under the cutter blades to raise the blades a few thousands.