I just removed the rear window from a '72 350 slc and it went very easily. Granted the seal was old and I did not try to save it so there was no special care needed. My slc has an aluminum molding around the glass that must come out first. If yours has this then be very careful before you start ripping and tearing.
I took mine out using a wide, flat pry bar called a Wunderbar. You must pry up very gently so as not to kink the molding. It is very soft. One bar on either side and a friend to help lift it out might work.
Once my molding was out I just ran a sharp knife around the outside and cut a way the old seal. Once you get the seal cut off the outside you can see the edge of the window. Cut down along side the glass. If your car is fairly new the seal should be soft enough that the window should just lift out. REMEMBER; if you have a rear window defroster there is a power cord. Mine comes out on the bottom passenger side corner. It unplugs through the trunk. Obviously if the back glass is broken you don't need to worry about this.
A faster way is to use a piece of stainless steel wire. Push the wire through the seal, tie each end to a short piece of wood as a handle, and then pull it around the window. It will cut the seal as slick as can be.
I just had a run around with the local glass shop about putting my glass back in. They put the window in and THEN tried to install the aluminum molding into the seal. It won't work this way. The molding HAS to be installed BEFORE the glass is put into the car.
Once the molding is in place you have to wrap a 1/8 to 1/4 in. rope around the lip that holds the seal into the car body. This opens the lip so that it will slip over the frame easily. Be sure that the two ends cross over at the bottom of the window. Place the window into the frame with the bottom lip in first. If you have a rear window defroster be sure that the wire goes in the hole and that
Be sure that the window is lined up in the center of the frame, i.e., that the corners will be in the right place once the window is in. Then while you get a friend to push down gently on the botton of the glass get inside the car and start pulling out the rope. This will bring the lip of the seal out over the frame and the glass should just pop in. One of those little hooked glass installer's tools will help bring the seal lip out over the frame.
ps. The little hooked took is also handy for grabbing the cajonies of little kids that throw rocks.