I've been over this in my head a thousand times.. and I think I could make some serious power by use a 10 hp block, horizontal, for a build for a Super Mod Lawn mower racer. You could use a ton of pulling parts.. And it is under the 28 CI rule for unlimited modifications.
But... the engine is heavy and tall.. I would rather use a side shaft so I could use a centrifugal clutch..
Anyone have a suggestion?