Interesting question...I have always on these 67-8's put the vent in first, adjusted to the window surround weatherstrip next, regulator & track like you mentioned, screwing the glass in next and adjust the glass to land on the window surround weatherstrip next, (weatherstips last, dropping glass very low with bumper/stop removed to allow access to the weatherstrip screws)
THERE MAY BE BETTER WAYS, I am curious to hear!