For what it's worth, since you were talking about weapons on vehicles stripped from aircraft, I remember seeing a pic of a WWII PT boat that had the 37mm autocannon from a P39 Airacobra rigged on a weapon mount on the deck, with traverse and elevation, fire controls, ammunition drum, the works. If they could do it on a boat, pretty sure they could have set up something similiar on a truck as well. Of course, I think you'd find 37mm ammunition to be fairly scarce these days.
Of course, not just guns. If you wanted to get fancier....they were for a while touting around the HUMRAAM, which was basically a Humvee modified to carry a turret rack that mounted (correct me if I'm wrong) 4 AMRAAM's and 2 Sidewinders modified for the SAM role.
Just goes to show I guess that with enough ingenuity, you can, within reason, pretty much mount ALMOST anything from an aircraft onto a vehicle, provided the vehicle is large enough and can handle the weight and recoil of the weapons. Of course, something like the 30mm Avenger autocannon mounted on the A-10 might be a bit problematic.
