How bout a support bar all the way at the back. You could make it fit into the supports back there and not have to drill any holes etc. i have also seen some pretty cool hitch engineering where u can slide something into a class 3.
Not mine but.... I thought I had a picture of this Scrambler with a kayak on the frame but I couldn't find it. I'll keep looking but you get the point. I remember reading a post on Facebook under the picture and the owner said with the canoe/kayak on top and some gear in the bed he could still see to back up, which was part of his plan when he built the rack.... I'll keep looking for that picture.
On my cj7's front bumper I welded a piece of metal gas line (probably 2"), then got a long (probably 1 1/2") and a screw flange. On the flange I bolted a 2' piece of 2x4. Set the height with the canoe on the roll bar and the 2x4, drilled a hole through the metal pipes. When I wanted to go fishing, I put the pipe in the bumper pipe, put a bolt through the hole, tossed the canoe on, strap and go. You can also do this combined with Randy's and you would be set. This setup was used in the 80's before Randy's setup was around.
Here's my cheap solution that has proven invaluable hauling not just a canoe but lumber (up to multiple 24' PT 2x10's).
The rack is made from a combination of top rail (chain link) and large diameter electrical conduit from the local big box store.
There are two 12" pieces bolted vertically just inside the tailgate... the rack slides in and out of those... nothing else secures it (although I do have some holes drilled through the vertical pieces to accept pins.