FWIW, early helicopters (Sikorsky R4 springs to mind) had only one collective, and the left seat pilot flew left handed, with his right hand on the common collective. This is often quoted as the "reason" that helicopters are (generally) flown command from the right seat, since this is the "natural" seat for a right handed person.
Since the R4 was so narrow that two people have trouble sitting side by side, the manipulation of the collective must have been a cosy arrangement.....
