one of the most numerous British bikes of the post-war era - the Bantam - had a cross-over drive. The clutch was on the right side of the engine unit, and the final drive on the left. This was BSA's version of the same DKW bike which formed the basis for the Hummer.
The same feature survived on the MZ two-strokes up their final models in, I think, the early 90s. These had an engine-speed clutch on the crankshaft of the 250cc units, but the older 150cc ones were again very similar to the Bantam/Hummer, being another DKW derivative.
The 1919 "Baby" Triumph had a cross-over transmission http://www.barkshire.co.uk/bikes/images ... %20005.jpg
although no clutch was fitted. I would suspect that if I knew enough about early belt-drive lightweights, there might be others.
Douglas in-line flat-twins also had a cross-over transmission, I have some photos somewhere ...
re the Sportster, yes it is indeed a unit motor so the transmission stresses are within the main castings. I have edited the original post "according". However comments about asymmetric loadings on the shafts and bearings stand.
Shoot, a man could have a good weekend in Dallas with all that stuff...