Are you asking how to install the dash vents, the dash pad, or both?
As far as the vents......I am not sure if there is any difference with the "pitch" of the dash between 68 and 69 which could affect installing the vents. I know the dashpad itself is different (68 has more of a "sharp" edge facing the passengers). But I definately did not remove the windshield, and I did not trim the bottom of the vents to install (trial and error with options on how you angle the vents). They use the four speed-nuts to hold in place.
After typing my previous post about the dashpad, I think I did remove the instrument cluster to replace the dash pad.
Also, I had replaced the glove-box cardboard box so that was probably out too. The radio might have been out as well.
The dashpad has studs attached to it - 6, I think, that are spaced out. they go into the holes in the steel dash frame. I used a 1/4 " driver (screwdriver handle 1/4 drive) with a 3/8" deep socket (i think it was 3/8, I did this back in '94 or '95).
First, with your hand digging around, find the stud, than use the tool to remove the nut. Do that for all 6.
Expect to get a sore back and right arm (if right handed) lol.
I hope this post makes sense...... :leave:
PM me if you want with questions, I'll try my best to help!