Dave did a great job with his B&S motor...
Also, this might not be exactly what you looking for but check out the master, Paul Brodie at work... he made an exact replica of a 1919 Excelsior Board Track Racer.
Flashback Fabrications Ltd.
He made the engine all by himself too. Not saying you going to do that but you might contact him...never know what he might say or have in the way of drawings or schematics! Either way his work will inspire anyone.