I replied to your PM, but for the sake of convenience, here ya go.
There should be enough slack in them so you have some wiggle room, however be cautious not to move it to much from the original position and cause the steering cable to be in a bind or wear out prematurely.
You might also check with Earmark, as well as Youdaman. I know he has several Moomba's in the gallery online and I can assure you they don't have truck boxes wedged in. Might be of some help.
Not sure if these pics help, but here is how mine is done. Of course, pre-planned it in paint. My dimensions ended up changing after this pic, but I didn't take the time to update the drawing.
I did not end up using the legs drawn in this picture. I used L brackets on the side, and compressed a few to less than a 90 degree bend and used them underneath, as well as attached thru the box to the hump.
This one shows how the box ends up elevated off the floor all the way to the hump, with the facade coming right past the box by and inch or so. Every inch of footroom is still there. After I built it, I realized I could have still made the box 2" deeper all the way around and gained alot more "size" but I wasn't sure so this is what I ended with.
The cutout on the right side of my box is where my heater hose comes thru to connect to the facade. On the side view, you can see the area of the hump that the box does not set on, that is where all my cables come thru. So everything is for the most part un-moved behind it in the factory position.
2006 Supra 20 - Sold
2006 Supra 24 Gravity Games - Sold
2015 Supra SE450 - Sold