Great job. Over the years of plowing snow off the drive, and wanting to do the same as you have done, I envy you with this side wing and may get motivated to do similar. However, my recent plow is a 7' western, and it has more width for getting the snow back where I need it. At least it doesn't fall back under the rear wheel when I plow.
About the 'float', I recall running a wing plow during a big storm about 15 years ago, and it was after re-stringing the cable that controlled the wing. Turned out we couldn't get all the slack out of the cable (it was an emergency replacement and too big for the pulleys) and that slack caused some difficult control problems. Being able to hold the wing in position turned out to be important.
This wing was on a large OshKosh truck with a big V-plow on front and the wing. I could get the wing down into the snow drifts by pulling it down to a point where it would then 'dive' into the snow drift and cause great concern to the driver. He would say "you're going to tip us over doing that!". So I would try to hold the wing up so it couldn't dive, but it would then just float on the snow drifts, and not cut in. Seemed it was either floating or diving, because of the slack. The driver attributed it to the 'rooky' wing man, but the next day when the regular wing man was on board, they learned real fast what I was having to put up with. The correct cable with no slack was the answer.
You may not have that much free travel nor have that problem, but Henro's solution sounds like a good design to have too.
There is a commercial outfit that makes a sidewing for pickup-type plows. Suspect they operate similar to the way yours operates. Nice job. Thanks for posting.