On my 67, I measured 34 1/2 inches from the bottom of the dome light lens to the tar paper on the top of the tunnel.
I also noticed that in the area near the back of the dome light, I can't push the roof down at all. Forward of the dome light, I can push the roof down maybe 1/8 inch before it hits some bracing. If I push on the roof area above the steering wheel, it goes down about 1/2 inch and pops back up when I let go - apparently no bracing in that area.
