Mark your distributor and the mounting bracket so you can get the same timing advance when you put the distributor back in. Two 12mm bolts hold the distributor in - one on top and one on the bottom. I always remove the cap before pulling hte distributor to give myself some room. Before you pull the distributor, note the position of the rotor so you can get this in the ball park when you reinstall it.
You can move the rotor back and forth when you are pushing the distributor back in to get the key to line up. As noted above, it only goes back in all the way at one rotor position. It should pop right in when properly aligned.