That's what I was thinking it was for but wasn't sure. Looks like a good place to mount a spare. Put the spare between that and the flatbed. Edit: I see Dan had the same thought as me.
No worries, just let me know on the adapters. I'll probably throw them up on pirate if you don't want them. I was totally going to use them so that the 4runner and trailer would be running the same size wheels and tires, but it ended up not making much sense due to me pulling it alot with the tacoma (it will be along time-never before it will see 33's) and the van will tow it once I get a hitch on it. That and the fact that I got such a great deal on the tires I have on it now and they will never wear out.