You need to remove the front bed rail as part of the install.
I went with the cross bin 8 because I didn’t want to lose all the vertical space. I haven’t used it for much yet, but bike gear.
Looks like roughly 6.5” above the first 2x4. In my case, I got one of the bins to fit under the front hatch, so I likely have less than the 6.5” at the center.
I have the HD, but I haven’t tried putting any lumber in there yet. I’ll be out of town this week, but I can check when I get back.
I believe you should be able to get at least one stack in there.