Leif...........that works for 49 and newer but my 48 installs from the inside as an assembly (glass and seal)and is held in place by the garnish molding while the sealer sets. I found a somewhat vague description in the 46-47 Fisher Body Manual pgs 71,72,180 @ the site that stock49 listed above....... http://chevy.oldcarmanualproject.com/
I knew about the string trick, but couldn't apply it to this situation...........thanks, Joe

OBTW, the pinch seal is separate and goes on first from the outside with adhesive and then it holds the reveal molding on.