I think the bolted crankshaft is better than the billet.
I've heard that the billet crankshaft and damage the engine because it does not deflect.
As an engineer (M.Sc.) I can tell you this is wrong. The deflection causes alternating circular loads on the bearings which of course transplants into the crankcase.
If these loads and deflections get large enough, the crankcases (esp. the drive side) will fracture due to fatigue.
For your engine and crankshaft, it is quite safe to assess these loads and deflections to be substantially higher than those of a standard motor.
An even greater concern is the size of the PTO shaft, which is really tiny for this kind of torque and load transfer. Please have your crankshaft journals and shafts carefully checked for micro-cracking using Eddy Current, penetrating dye and other NDT methods. Another change to consider is fitting a steel flywheel rather than the nodular cast iron F/W supplied by the factory. At 6500 rpm max your flywheel may not be at risk, but fitting one out of steel is one worry less. There are numerous articles on this site describing the virtues of a steel flywheel.
Many used crankshafts are near end of life, and survive only because the associated engines are never revved under full load.
I also put a note that a supplier has removed the billet crankshafts sales, I believe it to be a reason.
This is unfounded speculation. I am not sure which supplier you refer to. There can be a number of reasons for a business to close down or shift its product offerings.
Being pricey (from US$1900 upwards), billet crankshafts will never be a big runner with the average biker, power builders / racers and some dedicated enthusiasts exempted,
and let's be honest, the market for power accessories is with owners of japanese 4-cyl. machines.
-Knut