for those of us in the US of A, im actually thinking that the ECU can fit in the tail still, but if you have a lithium battery, maybe strip the charcoal canister, use it to mount the battery, and then use some fuel lines to disguise the wires. the only thing would be heat, but i think if you can put something that houses fuel vapors there, a battery would be fine.
Looking at it I may pick up a subframe and give it a shot. All it would take is a reposition of mounting points. Then making the plastics and seat fit. If I do this it likely won’t be till the new year, as I’m backed up on a current project