may take a few guesses to get the right one. it is a really a custom fit,to the vehicle deal. i run drop 6" on my dodge 2500 4x4,my dad runs flat on his 2x4 dodge 3500 and my brother in law runs up 8" on his kayak trailer behind a mazda 3 hatch back.
single axle you don't notice much. ran to high a hitch with our dual axle utility trail awhile and ate the rear tires up.
never really thought about the how the ball is mounted, but a locking pin is a good idea.