Paughco 746B 3.5qt Wrap Around Oil Tank Harley Davidson Big Twin.
Based on our research this is a Paughco wrap around oil tank. Part number 746B. According to Paughco “When used with an FXE battery, they’ll fit rigid and 1958–1964 swingarm frames, and will also clear 1979–up 4-speed transmissions. The tanks measure 5-5/8"-tall x 8-5/8"-deep x 12-1/4"-wide, and the battery compartment is 7-1/2" wide x 5-1/8"-deep.”
Chrome is rough and peeling. Would look good on an old chopper.
See photos. Sold as is.