I've never seen a boat trailer with a weight distributing hitch, because they all have surge brakes. The brakes would not work with that type of hitch. In that case, your 4Runner is only rated for 5,000# weight carrying & 500# tongue weight.
I tow 5,500 with a weight distributing hitch with ease.
To try it, you would need self leveling or air shocks to keep your back end from dragging.
Good luck