I have read a lot of posts here and elsewhere about redoing the body mounts. A couple of questions specifically about #4 that I haven't seen discussed:

To answer the first question, yes, you can do it that way. Of course, it takes two folks to remove/replace it like that.

As far as your second question, what support are you referring to? The plate riveted to the body for the mount nut cage? You could certainly use bolts/nuts there if you wanted, I s'pose, if there is enough clearance for them.

I also broke my #4 cage. To get it apart, I got an oversze socket that would fit the square nut. I used an extension to get up out of the recess area. I put the ratchet on then used a piece of pipe onto the ratchet handle. On the outside I tuned the bolt while holding onto the pipe end thru the door opening. I bought a new cage, but decided not to use it. I bought a grade 8 nut and used a heavy washer that I had left over from a shock replacement (or something). I did the same procedure to tighten everything down by myself.......so it can be done.   

The support I was referring to is the support at the #4 body mount that is in the wheelwell, exterior to the body.

I wish you had a picture of you working both ends of the bolt from the outside - priceless!

Yes indeedee that's the one. Getting it out was the hard part. With everything new getting it in wasn't bad. It sure would have been easier with two people.....but I kind of do everything myself.