Just did this last year on my 1952 3100 door glass. I removed that rail with a heavy duty heater gun "blow dryer" and removed the old glass, mark the original channel position on each end to get the new channel/glass the same measurement. This step is very important because if the measurement is off it will gouge and tear the verticle up and down channel besides the tear/gouge the window will not roll up without jamming. Found this out the hard way as I ordered new glass fitted improperly to my original rails. Had to heat up that rail and move it away from the verticle channel for proper clearance, after that a little teflon spray and that window rolls up and down solid, straight and really smooth. Lucky for me I had an extra verticle channel to replace the gouged/torn one. Good luck.
