Every time I've experienced a bike that favoured one side or the other, aligning the wheels has cured it. EVERY time. If it really was a motor placed out of line "laterally", shifting ones derriere to the opposite side would cure it. I may back down if shifting weight to the other side really works, but I don't expect to have to. Easy to find out...
The sole exception is the Sunbeam S7, which being a fore-and-aft crank (the motor was based on one designed by BSA in 1932 and called the line-ahead-twin, LAT) leans left or right depending on throttle action: whack it open and it leans right, close it, it leans left. Makes right-handers interesting, particularly if one can't maintain a steady throttle. Lean it in, shut off, it picks itself up. Open up to lift it up, it lies down. This is not concerting... But it goes wonderfully round left-handers.
Amazing that none of the "road test" reports of the day ever mentioned this...
Tom,
Perhaps they were afraid of the wrath of Bernard Law M.......... although there is no evidence he ever rode his.
Hugo