Here's my 2 cents worth.
A few years ago, I had a glass shop experienced in customs, street rods etc. replace my 544 windshield. They took out the seal with trim in place and put it back, telling me that the seal was in good condition. Shortly after, the seal started coming apart and they were willing to install a new one but would not tackle the trim.
After a lot of searching I found an out of town body shop willing to do the job. After 6 hours they gave up, having tried it with the the glass in and out, and badly damaging the trim, {which bends very easily.}
I ran an ad. on Craigs List: "Wanted - Old glass guy experienced with '60's Volvos" and found a retired glass guy who installed it in 20 minutes using the string method and an installer's tool with a twisted tip like a corkscrew.
Weeks later I found new trim to replace the battered original, and he agreed to do the replacement. It took 5 hours of sweating and cursing, trying it with the glass in and out! Eventually it worked best with the glass in in place.