Attempted this same project and ran into the same issues. Mine seem to be seized as well. Just like already mentioned the bolt turns, the top is loos and non binding, however the bolt just doesnt want to back out. Didnt have any more time to dedicate to the project today so bolted it back together and sprayed both sides real good.

One problem I noticed with protecting the threads and just hitting the end of the bolt is the bracket on the backside by the bolt head will start to bend. Afterall it is pretty thin metal for a mounting bracket.

Going to try a gear puller, or maybe vice grip the two brackets together so that when hitting the bolt it'll be more of a stiff assembly rather than the rear bracket taking all of the force.