Replacing 300cd quarter window, agonizing

[300cdwindow]

So, I disassembled the quarter window assembly from my 1980 300cd. I removed the window, regulator, guide rail, everything until the pocket was empty. Are there any tips for getting the actual window back in? Haynes makes it look so easy...
Here's what I gather to be the order of reassembly:
1. install rear rod (for the slider)
2. bolt in motor/ regulator
3. bolt slider to regulator
4. slide guide rail onto window
5. Slide window into place
This is where it breaks down. I can't get the window/guide rail assembly in. Three hours of trying every which way of cramming it in. The rail always slams into the regulator assembly or jams in the opening toward the driver's door. Should the guide rail be bolted in first? I don't see why this would be the case, as the stopper on the rail would wind up on the bottom, instead of at the top where it seems most apt. Help would be appreciated.