I helped my neighbor do his '57 rear window several years back, that's how we did it. Make sure the headliner is securely in place around the opening before you start so it doesn't shift or pucker out of place while the window is going in. The chrome trim was installed on the window seal before we started.
A small dia (3/16?) parachute type cord should work well. Put it snugly into the groove with the ends overlapping and hanging out at the bottom. Place the bottom of the seal, window and rope ends into the opening with as much of the seal lip inside as you can, then pull the cord in a bit at a time, alternating L & R sides around the window as it pulls the seal lip inside with it. Someone on the outside carefully pushing in at the same spot is very helpful.
The rubber seal we used was new, the opening thoroughly cleaned and the car isn't driven in the rain so potential leaks haven't been noticed. Other folks here have found a liquid caulk sealer helpful on some cars but I don't believe it's usually done on these windows.
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