Hi Joe . . .

The procedure is documented in the 49-53 manual which is available online at the Old Car Manual Project

It involves soaping the rubber lip that fits over the pinch weld and then putting a strong cord/twine into the gap between the window and the lip. The cord runs all the way around the window gasket with both ends coming together in one of the lower corners. Now with a helper holding the window over the opening - or some masking tape holding from the outside - the bottom corner with the string ends has the lip started in over the pinch weld. Next the strings are pulled from the inside to bring more and more of lip in and over the pinch weld. This progresses by working the perimeter a little in each direction from the corner where you started.

The manual doesn't say it but you don't want to end up in the opposite corner as it's to tight to bring that last bit of lip inside. Instead stop pulling the string about midway at the top of the window and work your way along the bottom and up the other side. With all four corners in you can work the lip on the top with both the sting ends.

regards,
stock49

[Linked Image from 49fastback.com]