Most tow hook setups use that big oval hole in one way or another, whether it's for the rear bolt, or the front bolt if the front section is in the way. I'd think you could mount those using the oval hole for the front bolt in those hooks, then drill the back. Use a big fat rectangular metal plate with a hole drilled in it to put inside the frame, and put the bolt through there too, then drop the bolt through the plate, down through the tow hook, and use the washer/nut on the bottom to pull it together.
If the bottom bumper mount hole sleeve is in the way of getting a bolt in there vertically using the oval hole for the rear bolt in the tow hook, I'd agree the location with the 2 x's might seem to be the easiest solution, but I think it's going to be a little weak since even though it's drilling through 2 layers at the seam, there might not be much material on either side once drilled though, making it so any kind of off-center pull would twist/distort the frame mounting point, particularly because of how close the forward hole is to the very end.
Maybe not, but if you have a way to weld, I would say fill in the outside part of the bottom seam, and then add another .120/.125 flat metal piece on bottom for a flat mount and extra strength. Even if you don't do it now, you could always add it later.
My vote would be for having the hooks kicked back using the oval hole for the front bolt, or even drilling both holes in front/back of that hole since it's the lowest part. There should be enough space between the front of the frame and the loop to make it useful, and having it back farther will keep it from being the thing that kills the approach angle or gets hung up on stuff.
