I never have seen a build thread on that bike but as mentioned, the battery is probably under the bum-stop of the seat. Ballistic Batteries are quite small for the same amps. I have also seen other builds where the battery was in box on top of the swingarm.
81 Honda CB750C - Current Project
67 BSA Spitfire MkIII - Next Up (Full Resto)
81 Honda GL1100 - Bob / CafeĀ“
80 Suzuki GS750L - Bratstyle
72 Honda CB450K5 - Basket Case
73 Honda CB350F Cafe' (Gone but not forgotten)
Don't wait for opportunity to knock... kick the door down and drag the old harlot in!