I went back and looked at the original post, you seem pretty hell bent on using the canoe carrier. I would recommend shortening it up so it falls in the middle of the span between the end of the chassis and the tailgate. Cantilevering that much weight, that far out makes for a lever arm that is going to break something when a big bump comes along. Make the vertical portion of it adjustable to keep the chassis level (or better yet, slightly taller so weight is transfered down, toward the back of the box.)
I would also try to run some straps to the canoe rack back to the tie downs In the bed to take some of the sag out of that assembly.
We have all done it, so we all know....but if it wiggles when you load it....it will come loose when you least expect it in transit.
It will be a cool trip, we did the RT. 66 trip in December. A few years back, speaking of being an ass.....stop in oatman AZ!