Thanks for the tips, gang. After a night of penetrating oil and a second try I was able to get it down. Very glad I braced the spare in three places when the last bolt gave way, otherwise It definitely would have mashed my head and chest... Getting the anti-theft pin out was not super easy, basically a brute force flathead screwdriver and rubber mallet attack on that compression washer thing all the way at the base, then I used a pair of pliers to grab it and pull it free. I completely agree with all others that said this: it is a terrible bit of engineering, the slightest mud or rust in there would render the key completely useless and you'd be completely stuck. Better to have this thing gone and take your chances with the thieves.
Thanks!
-Chris