Thanks guys. I am making some progress. Working on just the RA for now, I cut and tried a variety of shim material, including aluminium flashing material, and some thin galvanised steel strapping used in building. Backed off everything, and inserted the thin gal steel strip in between the motor carrier and the main drive casting. Once adjusted and locked down, effectively pushing the motor drive outward, it improved the situation a fair bit, with the belt now staying on the motor sprocket with no overhang. It will need some more refinement in coming days, to tune the angles and belt tension abit more, but i have had enough for now. At least its on a pier and easy to work on.
Edit: I am considering inserting a support block under the motor in the area indicated in orange, as the entire weight of the cantelivered engine and transmission is supported by the arm and secured with the lock down screws. Small movements in the shim area affect the angle of the rear of the motor (in red) and thus the running angle of the sprocket.