I did mention "sequential" as a bonus but didnt know they where
as strong as say an auto box like a 60 series datsun 5 speed.
In fact they must be able to take engine revs past 12000rpm and
most gearbox will self destruct changing gears up there, not to
mention the clutch and flywheels would be in your pedals.

Now for me its to find and affordable 1-1.3 litre motorbike engine
with 5 speed sequential that is strong enough for 500kg and be
able to be supercharged if only 8 valve or less than 105hp.