Replica chrome TT Bobber big twin oil tank is 1-5/16" shorter in order to accommodate a raised position for chain alignment.
The Purpose of tank is to raise the transmission and clutch pak for TT racing or hillclimbing for greater ground clearance. You can raise the transmission mount plate with 1-5/16" spacers and mount as stock. The battery compartment is shorter in this tank so a smaller battery is required. Chain guard will be in a raised position so modifications must be made to the front mount tab. Most TT bikes did not use a chain guard in the early racing era. Use (2) 3"x3/8" SAE bolts and (2) 2-1/2"x3/8" SAE bolts to mount transmission plate. Oil tank front mount on the frame must be removed and re-welded in place 1.25" upward. Use a spacer, 5 required, on the 5th mount bolt (1) 2"x2/8" NC. *NOTE: Tank is not designed for electric start installations.

Fits: 

Custom application for Rigid frame
EL 1936-1952
FL 1941-1957