Steve,
It is certainly easier to remove and replace the frame and windshield if the dashboard is out. However, the windshield and frame can be removed with the dashboard in place. Unless you are thin and very flexible, the easiest way is to remove the seats. Removal of the steering wheel also makes it somewhat easier. All of that should only take a few minutes if the attaching hardware is in good shape. With a nice soft quilt, maybe a pillow also on the floor and over draped over the pedals, you can lie on your back and look up at the three most difficult fasteners. A small 1/4 inch ratchet and a long extension work well in removing the nuts. The remaining two fasteners are right at the edges by the doors and can be reached without major difficulty. Two people make the job much easier in removal and resetting. This is not intended to make light of the time and level of difficulty of getting the two gaskets positioned correctly. That can take a lot of patience, glue and duct tape until the glue dries. I have had the most success positioning the gasket properly on the windshield, working my way around the windshield and using small dabs of super glue under the gasket to hold it in place. Note you must thoroughly clean the glass and particularly the gasket to remove the mold release agent or nothing will stick well.
Dave Lawler