The repair/rework of this area can lead you down a slippery slope. You will need to decide how far you want to explore.
The 7 clips referred to provide support for the back edge of the cowl piece and maintain alignment with the bottom of the windscreen trim. The front pop rivets you removed secure the front edge of the piece. On my car the front edge was secured with sheet metal screws and spring nuts on the back side of the body lip. Without the 7 clips, there is no way to hold the back edge of the cowl straight. I would be concerned about reinstalling without putting the clips back in place. I would be a little bit concerned about this area since the clips have completely rusted away. Makes you wonder what else has rusted that you cannot see.
I have enclosed a couple of photos of the conditions I found on the Spiders I have been working on.
The next step as Series4 said, is to remove the windscreen. That involves removing the chrome trim on the front and sides and the plastic trim on the inside plus the rear view mirror. Then the wind screen must come out along with the rubber perimeter gasket. Once everything is out, you can determine the extent of the repairs required.
Are you located near any AlfaBB members that could assist you with this?
I found some disturbing conditions under one of my cars that will need extensive repairs. I was very glad that I explored this area. On my 74, the area was beginning to rust and I was able to clean it up and coat it with several applications of epoxy primer.
There are some techniques that will make the removal and install of the windscreen easier. Let us know if you decide to do a little exploration.
76 starting to show some signs of rust.
74 that looked similar to the 76 above, cleaned and primed
80 that has rusted through on passenger side. This will require new sheet metal to be cut, fit and welded in place.
80 drivers side will require extensive repair to strengthen the windscreen frame and deal with the rusted fender area.
Cowl area of the 74 before starting work on it.
I hope this helps.