After I posted my reply i continued to research and found both your build (very long but worth every page of information), and CAMNZ's build. I liked your thread better because you posted so much information. I'm thinking about making account over on motorbicycling.com to follow our build.
I was not going to use a centrifugal clutch. I can't stand them on a motorised bike, its just not how they are supposed to be, I will be using a tensioner on the primary belt similar to yours. I love your lever idea on your tensioner. Looks really old school

How does it stay forward when you put tension on it? Is there some sort of lock on it? I have a really small drive pulley for the engine, about 2'? Its very small, so thanks to you i'll use that one

My engine has no starting mechanism, no kick starter or rope starter. So i have no choice but to pedal start.
I think i could fab up a straight pipe that sounds real nice, my ucle has a TIG welder so i should be able to weld up a pretty one
And also, do happen to have any spares for these little engines? My engine is missing its ignition system inside the flywheel. It still has the coil but the points and every thing else are gone

My dad's friend may have a spare one of these engines but im not sure so im sorta no the lookout for any parts.