I finally tackled this project.
Step negative 1: choose a weekend without tropical storm warnings if working outside.
Step 1: Remove bolts from underside of assembly (headliner already removed) and drain hoses.
Remove assembly (shaved 42 lbs off top of car).
Step 2: Identify roof support bands both front and back of sunroof hole.
Step 3: Carefully cut 3/4" back all around sunroof hole. Make sure only to cut through top level of sheet metal. Take out 6" sections at a time by making cross cuts. After you have cut a section for removal, I used a dulled chisel to remove it from the seam sealant on the bottom. The top sheet metal of the roof has a rolled lip over the roof support bands.
Clean up the old seam sealant and you have a nice flange for dropping in the new metal.
Step 4: Make a template of cut sunroof opening out of cardboard. Place old roof panel on car to match c900 curvature. Sharpie the sheetmetal in position on the roof from the inside. Take new roof panel off, position cardboard template in orientation to previously sharpied line. Draw new outline on metal (should be approximately 3/4" larger than old lines).
Cut with nibbler. Fine tune shape with 4" grinder.
Step 5: Run a generous bead of seam sealant all the way around the gap.
All and all, it was pretty easy. I was excited to find the roof support bars so I didn't have to flange the roof at all.
Jesus H. Tapdancin Christ,...