Reasonably easy.

I've worked with the old sticky black butyl rubber. To protect the glass try to use wood and plastic tools rather than metal. Eg. Instead of wire try strong fishing line tied around wood doweling.

Side windows down, poke a hole through the butyl, feed the line through, tie it around dowel or grip it with vise grips, draw it along the sides and top, inserting twigs or whatever into gap to prevent glass from resticking. Then tip it over onto the hood.

Haven't worked with the newer polyurethane but process is the same.

On re-installation, you may have to use polyurethane, as the old stuff may be hard to find. I think the 3M butyl tape is called "window weld"
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1980 245 Canadian B21A with SU carb but electronic ignition and M46 trans in Brampton, Ont.

Old style with metal trim or newer without trim?
Search internet for step-by-step methods and tools.
It is a good opportunity to seal all the gaps and guarantee no leaks.
In addition, there are drain holes at the bottom corners under the trim of my '81.