Anyway you look at it, it's still difficult to lift that boat up there on the roof, even more so when you lift your Liberty.
I'd build the cross bar out of tube steel. Get yourself an angle grinder and cutting wheel
There are some solutions like the Thule Outrigger II or Yakima's equivalent. They are steel rods that slide inside the main crossbar tubes so you can rest half of the boat on it while you lift the other end. This way you have to lift approximately half the weight of the boat.
You might want to build this into your system. Lifting 60 - 80 pounds of boat above 70 inches or so by yourself gets old real fast.
Take a look at various demo videos on Youtube to see which style of carriers work best for you, THEN you can make the bars that facilitate the style of loading you want (side loading vs rear loading).
Hull Raiser demo
Thule Outrigger II demo
I have the J-style carrier on my lifted KJ, sitting on top of a roof rack and the first words out of the guys that helped me carry the yak to my KJ were "oh, that's a little high"

It's near impossible to load / unload by myself. The carriers now sit on my wife's KJ where it's more manageable, but still needs two people to load / unload so I'm going to have to do something about it, either change to keel-down style and load from the rear, maybe use two outriggers and flip the boat onto the carrier, or buy me a hullavator, but that costs a lot of money ...