It is something someone put together, there were pictures of a similarly equipped David Bradley on the inter webs 3 or 4 years ago.
I don't think it was actually intended to be run with both bars mounted but a few old saws were setup so you could mount the bar in two locations.
Most all big Mac gear drives from the early to late 60's such as the 1-60 series,1-80 series,890/895 etc you could reverse the bar studs & change the main gear around to have the bar on the outside,such as for low stumping/other uses.
