My first attempt was with the vent window fully installed. Obviously this was a mistake because you can't fit the "upper loop" of the regulator in the correct spot with the vent wing post in place.
Next, I tried with the regulator partially mounted (just the 2 bolts fastened near the crank). This didn't work either, as the post mounting bracket hits the first cross-brace(?) piece of metal near the window opening.
Third, I tried a hybrid approach with the vent wing post inserted but the frame leaning back (away from the front of the car) so as to give the regulator "upper loop" enough space to fit into place. Once fastened, the vent wing frame would not pivot into place; the vent wing window "hinge bracket" (underneath frame) hits the second cross-brace(?) piece of metal nearest the front corner of the window.
Here's an annotated photo to hopefully take the guesswork out of my descriptions.

I'd really appreciate any guidance you could offer. Repairing this window has been a long, drawn-out process. I feel like I'm really close to finishing this and moving on to the next big project but this particular task is sucking the life out of me.