G'day Norm,
Well, these L-head sidevalves have both valves on the same side of the bore, as you know.
Carby and muffler on the same side is usual for the horizontal shaft L-heads, but has also been used on many vertical shaft models.
The most commonly found example of this setup in Oz, was the old Kirby-Lauson LV and VK series push mower engines, back in the day. Then later on, Kirby-Tecumseh and US Tecumseh engines.
Also commonly found on the bigger [over 5 hp] Briggs vertical shaft L-heads, that used Flo-Jet float carbies, as used on ride-ons.
As to why it's done, basically to reduce manufacturing cost.
It costs more to incorporate an intake crossover pipe in the design; but it's necessary to do so, with fuel tank mounted diaphragm carbies on vertical shaft engines. Briggs have just continued this practice on their later float carby L-head verticals, e.g. the Quantum series.
AFAIK Tecumseh never used a tank mounted diaphragm carby setup on their L-head verticals, so they just stuck with the 'same side' configuration.
