VW, we used a similar system when I was a kid, but it was an old 51 Chevy pickup that had originally been a wrecker. The hand throttle on the dash for operating the winch which had been left on it. Like you we made a trough just wide enough for the wheel to fit in, and jacked up the wheel just high enough there was room for a hulled walnut to pass under it. Of course we blocked the other wheels, and set it to a fast idle, then would throw nuts down the trough where they would go under the snow tire and be kicked out the rear. Occasionally one would fail to go through, and we would have to take a stick and jab it to get it to go under the wheel. The hulls would only go 3 or 4 feet, but the walnuts would go several feet, so we propped up an old binder canvas for a backstop to catch the walnuts. After we hulled a big batch we just had to take a scoop shovel and fill tow sacks to hang them in the shed with a wire to dry. Occasionally a squirrel would spot the sacks hanging in the open shed and worry itself to death trying to get to the walnuts, but as soon as the dog spotted him, he had better be fast.