The 3 pin driver for the Quietlines have a flex plate in the center that allowed for engine movement because of the ISO setup.
That flex plate usually ends up cracking after the ISO mounts go bad due to
excessive engine movement.
If you are going with solid mounts you won't have any engine movement, therefore you can use the solid 3 pin driver for non-ISO Cubs.
They are much cheaper and more available. You can find them used and new easily on eBay.
https://www.ebay.com/itm/27520219558...MAAOSwGHJiKJiP
https://www.ebay.com/itm/27503122218...gAAOSw6HhhlPMy
https://www.ebay.com/itm/25548037061...8AAOSw4lZiUfI9
https://www.ebay.com/itm/28476760468...sAAOSwpr1iWXFZ