How do you apply the sealant between the body and the gasket? I'm installing the back glass in the '66 this weekend too, but was planning on doing it the other way - gasket installed on the body, then installing the glass.
I am not an expert but I have read and watched as many videos as I could find. Every car is different and so is the way people have made it work.
The general rule for Darts looks like on the rear glass: ((Gasket on the glass and then work the rubber on to the pinch weld.)) The very first step is to use a caulk gun to put sealant in the gasket channel and then put the glass into the same channel. Use the rope method or another technique and pull the gasket (glass is in the gasket) into place from the inside. (Glass and the gasket are laying on the outside of the rear pinch weld.) After the glsss is installed you can peal/lift the rubber on the outside and in my case I have the little pump with a small spout that attaches to add the additional sealant between the rubber and the metal body.
Clear as mud???