it
is painful Jon

the vent needs to not only be loose, but be part way out when the glass goes in, and everything then pushes down together ... the regulator arms need to be in a position in front of the opening so the track can be slipped on the rollers, and when ready, the screws installed, but there's nothing to hold it - once the vent and window are slipped into place everything has to be held from moving while you put those screws in to secure the window to the track .... it does help to have extra hands, and it does help to take a break when ya start grinding yer teeth!
Bill