I suppose you could fit a Victa power torque motor.
But i would be looking at fitting an older full crank engine instead.
You would need to get a custom pulley made up. A replica of the greenfields that will fit on the Victa motor. Victa engines only have a short shaft.
The only issue then is that you are going from 10.5Hp back down to 5hp.
You would be better off with a Suzuki two stroke off a Rover.
The mastercut 600 is push only. The motors are plenty on one of them and they are easy to push despite their size.
Im actually glad that a bigger say 8-12hp two stroke is not commonly available, If it were my back yard and shed would be overflowing, i would want to keep them all.
I have thought of modifying a motorbike engine. A single cyl 400cc would run nice on its side with the carb turned round. Ignition could stay as is, just need a new crankpin for the primary drive side. Cut the gearbox off.