As someone who does this kind of work, the timeline is absolutely insane. The aircraft started out as a PZL-104MA Wilga 2000 but he redid part of the wing, built an entire carbon fiber cowling and redid the wiring, all on top of the engine install, though that and the carbon fiber he had fairly extensive previous experience with. One thing you'll notice if you watch the build videos is he makes extensive use of very complex CNC machining for the wing tip extensions and some other odds and ends. I would be very interested to know how much risk management went into the design though, as on the surface DRACO and Turbulence (his other PT-6 project) seem to have a lot eyeball engineering going on as neither airframe was ever designed to handle the flight loads that the engines put on them. There's only so much you can see in YouTube videos though so I'll give him the benefit of a doubt.