Glass removal

I use plastic tools to lift the gasket from the glass. The sealant will slowly seperate but it will bond right back too in most cases. Spray silicone lubricant will prevent that.
Once I get the gasket loose all the way around inside and out 2 or 4 feet against the upper inside of the glass and push slowly and evenly.
To be honest, cracking the front glass can be a hidden blessing. A new and clear front glass makes the results much more satisfying and worth the effort when complete.
I spend many hours with plastic tools and charcoal starter fluid and rags cleaning the original gaskets for reuse.
Extra time, money, and labor went into replacing the vent box seals, wiper pivot seals, etc.. But aAll the more satisfying results. Inside of my 67 stays bone dry.