Over four decades, I have restored a number of 1965 & 1966 Buick Skylark GranSports and removed many windshields from many different cars. Each has their own little styling quirks that can make the removal a challenge. Especially if you need to save the windshild...rear window is no different.
There are tools made specifically for windshield removal. Most have an assortment of different length blades for different cars/trucks. Best place to look at one, touch one and get the feel of it is a automotive paint store. They usually carry a few different brands. I can tell you now, a good unit will run you anywhere from $200 to $300 bucks. You can purchase a cheaper one for ocassional use for about $150 bucks but it will not have the motor/power and strokes per minute of a good one. You can look online for one, just do a search. These days, you might find a good deal...a model close out or overstock with a company.
Of course, you can always resort to the old method of windshield removal...piano wire. Takes two people, but you do get a clean cut with it.
Also, many automotive glass repair companies will pay a visit and remove a windshield for you. They usually charge $50 to $75 bucks in our neck of the woods. You can also visit one of your local body shops, many have the windshield removal tool. They may charge you much less, maybe nothing to cut a windshield out as a good will gesture. Bring a roll of duck tape with you. When they finish cutting the windshild out and it is loose, duck tape around the edges and drive the vehicle to the place you plan to install the new windshield. The windshield may be a little stuck as the blade really heats up the sealing compound, but it should still come out fairly easily with a little pushing from inside.
Whatever you do though, be careful. If the glass shatters, as you probably know it makes quite a mess and you do not want glass falling into the defrost vents....