I took regulator out of spare door and confirmed the only up stop is that plastic cylinder on rear of glass. Thats the only up stop there is. Took regulator out of door on car and no affect on vent to glass up stop alignment.
Someone on '67-'69 Barracuda group on facebook told me to tilt vent window back then move vent window forward and up. I was not seeing that as a fix when I first read that suggestion or your suggestion above.
However, I believe if vent is tilted back, then moved up and forward, that will tilt rear of glass down which will delay when the button on rear of glass hits up stop arm in door. So I believe vent glass adjustment is the solution based on suggestions along with monkeying around with the doors.
Note right now gap between A pillar and vent window is uniform right now on passengers door. But on driver's door, which glass has perfect fit, it looks like vent frame is tilted back a tad, minor ununiform gap, but its not something anyone will notice at all.
