You might want to check with a good glass shop, as they do this all the time.

When I did this in my 250C, I installed and supported the new channel, lined up the window, and pounded on it with a rubber mallet until it was seated. I think I sprayed the channel with silicon to help the glass slide in.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe