If you can get the spindle nut off with that Breaker Bar that's just chillin. ) Auto-Zone or Checker, someplace like that rents tools. See if they have a Big Slide Hammer that you can use to pull that spindle out enough to get the new stud in. It should be a Big Slide Hammer tool that connects by using the axle studs, just pull the spindle out enough to give you the room to put the new stud in.
Yep it's then disk conversion that is causing you problems. You're going to have to take the outer u-joint loose, take the stub axle nut off and jerk the stub axle out with a slide hammer some to get the stud in. That's -IF- the stub axle will come out some. Many times they are frozen into the bearings. You might have to take the whole corner out of the car to get it pressed out.
Personaly I (This is just me) would take both sides down and install new studs. At the sametime I would cut off a section of the rear disk bracket to leave 3 mounting holes and make the brackets a slip on and off deal. This can aid you in a few different ways in the future... # bolts will hold the bracket securely with no problems..
The more I think about it the more I want to just take both rear corners out and get the axles pressed out and the spindle pins while I'm at it. It's one of those "as long as I've got it out I may as well..." situations that will probably end in me rebuilding everything on the rear suspension (it needs it) My springs and shocks are all shot to ****. :-/ [opens wallet]