The opening in the S90 frame to get a battery into is pretty small, so I have been searching what possible batteries could fit in there. It was either a 6V-7ah or a 12V-3ah unit. Then I had to make a choice on ignition coils, 6v or 12v and take into consideration that my rev-counter uses 12 volts.
In some old stuff from my dad's CB72's I found some original coils and brackets that looked like the coil on a CS90RSC that must have been raced with factory assistance. And so the choice was made to run a 12V system with battery-ignition without charging system.
Original CB72 Denso coils and brackets
Mounted on the frame, not on top of the engine.
Holes drilled from the inside to clear the internals of the frame. Bolts will be replaced with hex bolts.
Painted in the correct colours the shape of the bracket stands out better, and now I can even recognise the shape of the top of the bracket in the old RSC pictures. I would be surprised if honda used something else then CB72 coils for their RSC.