I helped the glass man on the windshield install on my '72 ES.
First we put the gasket on the window.
Then he sprayed the trim channel with window cleaner,
put his nylon line in the trim channel,and pulled the
line as we slipped the trim surround into the channel,
working it with the trim bone.
Then we put the window in.
Next he shot urethane sealant in under the glass side of the gasket
to seal it,and butyl flex around the outer channel,so the window
could be removed without breaking it. {my choice}
What a mess!! 1/2 a roll of paper towell and some wax and grease
remover later it looked great.
Yes, you might have to take the window out to get the trim on.
Try the 'rope trick' to open the trim channel either way.
Good luck,and as Tom said,patience is the key.
Ken
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White 86-245 DL, M 46, IPD bars & Wagon Overloads,Commando Bumpers,SS Belly Pan & Air Pickup,Straight-Shot EMT Chassis & Tower Braces,Scorpius Alloys,2 Belt No AC Conversion,Black POR-15 No Glare Front End