It's not hard to install new glass. But, it's already in the car. Here is the steps, but, beware, you can also easily break it with the wrong move. NEVER pry on the glass, tap on it etc. Read steps #1 and #8 before starting.
1) With the old glass out, install a new gasket/seal onto the new glass (plan ahead and order it with new moulding clips too)
2) Make sure the channel where the glass goes is clean of old sealer. Do Not use laquer thinner - you'll take the paint off. Use wax & grease remover.
3)Have enough rope, 1/4" size, to go around the perimeter of the glass plus a foot or so. Install this rope into the seal in the groove that the metal of the car will sit. Tape the excess to the glass toward the center of the glass on the inside to keep it out of the wrong place. Also, have the ends stop opposite of the roof and the ends centered.
4) Lay the glass, seal, rope onto the car in the area where it goes. Double check that it is centered.
5) Go inside the car and pull the rope so that it lifts the lip of the new seal over the metal lip. This moves the lip to the inside of the metal. Continue to the corners. The hard part was getting the seal/rope to go around the corner so don't use old crappy rope. If it breaks, you'll have to then try to get the glass out and the new seal. Hard to do. And be very careful here.
6) Work the seal to where it goes, inside and out (without prying!) I used needle nosed pliers to pull on it to fit - carefully, you don't want to tear the seal.
7) Caulk between the body and the new seal. I've seen this caulk at Advanced Auto Parts but I am sure other parts stores have it. 3M Bedding caulk
8) Push the new moulding clips into place (Ok, I should have mentioned to mark the stud location before laying the glass in. Use either a wax pencil or masking tape before laying in the glass. Also, it you have rusted off studs, this is the time to use the screws to hold the clips)
9) Install the mouldings. Push gently, or, use your palm to smack it down. Again, careful so you don't dent it, or, break your new glass.
If you boo-boo, well, that just cost you about $400, and one months wait time for the glass.
Get out the windex 'cause you are all done.