(assuming you are working on '57 Ford wagon)....If your top interior windshield garnish moulding has the clips with teeth on them to hold the headliner in place, it is not necessary to install the headliner first. Go ahead and put in your new windshield, then install front of headliner. It is always best to begin headliner installation at the front and install interior windshield garnish mouldings right away to hold headliner in place so you can stretch the material back and put headliner bows in one-by-one. Once you get to the very rear of wagon headliner, they have tabs above the liftgate framework you can use to clamp the back of headliner to the body.
If you were working on any '50's Ford Sedan or hardtop, you must have the rear window glass removed prior to headliner installation because the headliner material needs to be stretched and glued around the window channel first, then the window gasket covers over it. The window gasket is the only thing holding the rear of headliners on sedans and hardtops.
