I took a couple of pics with an old housing, can't really see a lot. Maybe they didn't have the holes pre-punched/drilled in '69 since it was the first year for the underdash? I know how it mounts in the '71.
The mounting studs are 14-3/8 inches apart on-center. The holes in the channel are 7/8 inches to the center from the back of the channel, tape hooked on back edge.
Find the centerline of the dash then measure 9-5/8 inches to the right for the centerline of the hole in the channel on the right and 4-3/4 inches to the center for the hole on the left. The front holes you mark when you test fit the housing. The center of the dash is the left side of the blue tape in the pic, to double-check the center is 3-1/8 inches from the left end of the piece that projects out of the front and fits under the dash between the front pad or surround. If all goes well I'll have mine in completely on Friday if you want a pic of that. Does your car have AC? Those front tabs are covered by the valance if so, some of the bracing has to be cut off the back of the valance after it's cut off to fit around them.
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