The concept is probably better suited for a dedicated design (i.e. the 'little & large' engine configuration mentioned previously, with input shafts rated accordingly) rather than an adaptation of an existing platform.
Yes, I Think your both right Ian and John.
The enlarged MGB and bigger engine weighs more and costs more, and it doesnt add payload. It eats from the payload availabe, as the Quick start mechanism do.
More expensive, less payload.