The damper on an auto crank is to stop the "ringing" of the crank set up by torsion loads applied by the con rods as the various cylinders fire. At harmonic RPM the rwisting can accelerate to the point that the crank twists apart; the vibratory loads are much higher than the engine's torque output. Vibration analysis is a huge and complex field all to itself, and engineers have earned doctorates studying it.
An aircraft engine's internal counterweights are mounted rather loosely on the crnk and are to absorb and later reinsert the torque pulses. Not the same thing at all as the rubber-mounted damper pulley ring found on your car.
Steve Wittman adapted an aluminum Buick V-8 to his Tailwind, inverted direct-drive. He used the bell housing to support a bearing and shaft assembly to isolate thrust and gyroscopic loads from the crank. However, this is not as simple as it sounds; the crank needs a flywheel of some sort, and if the propeller is it, then that shaft has to take severe forward-reverse torque loads from the crank and damp them out. Every time a cylinder fires there's a forward lurch; every time there's a compression load there's a reverse braking. The flywheel absorbs and returns those, and if those loads have to pass through a shaft, that shaft had better be REALLY stout. If we use a flywheel on the engine, then the shaft to the prop, the prop and flywheel have different ideas about damping and they get into an argument at certain RPMs and place huge loads on that shaft, which usually gives up and separates.
The PSRU has to deal with those loads. The old V-belts used years ago would slip and release the worst of the overloading. Toothed timing belts will get their teeth torn off if the designer doesn't get it right, and the PSRU we had on the Glastar's Soob told us that 1400 engine RPM was something to avoid. Spur gears suffer the worst, since only one tooth, maximum of two, is taking the load much of the time. Planetaries are much stronger and much heavier. Geschwender used the Morris Hy-Vo self-tensioning chain to good effect and those engines (Ford 351s) saw service in crop sprayers like the Pawnee.
Steve Wittman, as I heard it, eventually gave up on that Buick and put a Lyc in the airplane. Too much hassle, not the least of which is draining the oil out of the case and back to the tank without getting excessive oil bleed past the rings after shutdown, which can promptly flood the plugs (no restart, see?) and can cause hydraulic lock. Properly-designed inverted aircraft engines have the cylinder sleeves extending into the case an inch or so to act as oil dams, and also have several scavenge pumps to draw the oil out.