Dunno GB. The production Audi/VW V10 diesel as in Toauregs or whatever they're called has two banks of five in a line. Guess it all depends on the geometry down below, the piston size and width to allow rods to waggle and wiggle within (or not) and all that. Maybe they wanted a shorter block so they could shoe-horn it into a Golf ! ! !
Who knows?
Hell of a complicated piece of kit, whatever! Don't want anything of that on my bench.
The Puch thing, are you talking the 'split single'? There are a few of them about round here and they have their fans (as all things should) - but I'm too ignorant to be one. When talking 'fore-and-aft-twin' my mind is irrevocably captured (captivated even) by Douglas.