The oil bag is in what you would assume is the gas tank.One half is gas with an inner bulge passing thru the frame & into the space of the of the other 1/2 of the tank. The other shell has less capacity even though it appears equal from the exterior.A piece of trivia, that cool little dimple/inner tank is a tear drop shape 12" long & 4" tall. It was used as the cover for the dual card set up on Joe Petrali's/Daytona land speed recorder holder.
anyone know?... the back horizontal tube generally fitted in between rear upper and lowers on the WR frame... why did some not have it