That is a flux capacitor that's hooked to the transmission to activate the rest of the system at 88 MPH. Yeah,^^^^^what he said^^^^^. I am Butch/56sedandelivery.
I have a couple of them kicking around, I think they are part of the old tach drive of the distributor. Sent from my SM-G930V using The H.A.M.B. mobile app
Old Stewart-Warners from 30's and 40's had these angle adapters right at the backside of the tach or speedo. Many times they are removed and the poor next owner of the tach or speedo needs to round one up before he can use his purchase. If you don't need it, list it in the cl***ifieds and I'm sure you could get $25 for it.