Well, I guess I just needed a little more muscle... and a bigger wrench. Got the bolt off, but getting the housing for the bolts off the axle far enough to get the old bolts off was a pain. Of course getting it back in was another head-ache. Thankfully, the new bolts had cropped heads so the axle didn't get in the way of installing them. Pulled the bolts all the way through using the lug nuts, and the wheel for support. We'll see how well it holds on my 800+ mile trip this weekend.