"It seems to me you'd be better off changing the truck than the ramp.   Presumably the ramp hooks onto the back of the truck with some kind of mechanism.  I don't think it would be hard to weld up an adapter that hooked onto the truck all the way across the back and provided 3 anchor points for the ramp at different angles.  In the center the ramp should anchor straight out and on the sides at some slight angle.  2"