Are you determined to keep the flywheel and clutch?
With the pto and the original clutch centre you can mate the motor to the trans directly without the flywheel and clutch.
My immediate concern with using the pto centre on the motor shaft to support the flywheel is that it would not be a tight fit and would allow the flywheel to move and wobble. Even if you drilled and put in set screws I don't think it would give a tight enough fixing and also it would then not be as well centred.
I would recommend using a rigid attachment like a taper lock bush to clamp around the motor shaft. The flywheel could then be bolted to that either with its own set of bolts or with bolts that also do the clamping.
Others may well have their own take on this though.
With the pto and the original clutch centre you can mate the motor to the trans directly without the flywheel and clutch.
My immediate concern with using the pto centre on the motor shaft to support the flywheel is that it would not be a tight fit and would allow the flywheel to move and wobble. Even if you drilled and put in set screws I don't think it would give a tight enough fixing and also it would then not be as well centred.
I would recommend using a rigid attachment like a taper lock bush to clamp around the motor shaft. The flywheel could then be bolted to that either with its own set of bolts or with bolts that also do the clamping.
Others may well have their own take on this though.