I want to hang a tire swing my my deck - in the photo those are 4 6x6 vertical supports and 2x10 horizontal beams (sandwiched together) at the back and front of the deck.

This is the hardware I want to use:

http://www.playkids.com/-strse-2041/Tire-Swivel-Wood-Beam/Detail.bok

It's a 3"x6" plate with 1/2" holes.

I can't attach it under the front 2x10 beams as the screw holes would line up with the little gap between the sandwiched 2x10s.

I thought of running a 4x4 from the rear 2x10s to the front 2x10s then extending it a few feet out front of deck. But I'm not sure the best way to attach it. Or whether a short piece of 4x4 just attached somehow to the front 2x10 beam would work.

I'd like to tire swing to be able to hold 200lb but in practice it'd hold about 100lb.

Any advice or direction would be most appreciated.

Thanks.