If you go to my build thread (78 Wagoneer, building a driver) on page 48, post 958, I talk about how I did mine. If you are using a new lower gasket for the small window, I soaped it down and pushed it down into the door. then you can get enough angle to get the big glass in.
If you are reusing that lower gasket that holds the small glass in place, Kaiser Jeep left it out, used tape to hold the glass in place. Once the big glass was installed, he was able to slide the old gasket back in. His gasket was to hard to pass threw the inner and outer door skin. My new gasket was flexible enough to be pushed into the door with soapy water as a lubricate. hope this helps.
401/turbo 400 trans. Quadra-Trac BW1339 (with Low) 4" Rusty's lift with 31" Summit Mud Dawgs
Fuel Tank, Red Holley Fuel Pump, Razor Grill (profile pic out dated), Rebuilt steering box