I found a deal on some new windshields, and also scored some original window rubber in excellent condition. I have never removed/replaced front glass before, and don't understand the lockstrips. The cars in question are 69 Dart and 69 Satellite.

Did all Mopars with window gaskets use lockstrips? At what point in the installation sequence do you install them?

Lockstrips go in last. The gasket is installed, the glass seated, then the lockstrip is wedged into the gap in the outside surface of the gasket to lock the glass in the gasket. Not all used them, but it does make installing a gasketed glass easier. There are a couple different tools to insert the lockstrip, but even with them it's a pain until you have lots of practice.
Mike