Here's a picture of an old grapple that uses a single cylinder that has the barrel anchored to the legs and the rod anchored to the head. the hydraulic oil is pumped through oil galleries in the rod (those were fun to drill).
On a model the cylinder could be replaced with a screw drive to achieve the same effect with plenty of holding power.
The grapple was built by Chapman industries but didn't fair well because the rod was weak.
