Harry, I would remove the windscreen entirely. That way you'll get familiar with those brackets underneath, and can clean them up and oil them (for the next guy in 15 years), and you can replace that rubber gasket underneath the windscreen as well. $25 from Moss.
About those brackets under the dash--if they're frozen you can remove the bolts, grease them up, then rotate back and forth by applying a good wrench over a rag to avoid marring them.
Back to the windscreen assuming not already moot: Another reason to remove it is that you will want everything clean, and plenty of room to work and be set with your heater vents ready to re-fasten, the vertical dash screws that go back up into the dash frame, etc. I also found this to be an easy system for the glue stage. I'm trying to recall but believe I used a silicone glue on the upper part of the dash (sparingly as it doesn't need much at all), and contact cement on the flap that wraps back up under the dash. I wanted that tight, no wrinkles, smooth and clean.
I also wanted another person there to be sure the dash was fitted square and the windscreen fitted correctly as well.
Everyone has their own system so whatever works best for you. Good luck.