Well lubricated stainless steel fasteners (both on assembly and removal) and properly lined up fixing holes make the cowl removal and replacement a doddle.
When I rebuilt the 4/4 I spent quite a bit of time getting the cowl set up correctly so it could be easily removed and replaced before I painted the car.
Following on from Buttons suggestion. I used long 2BA stainless set screws with a hex head where space was limited so I could put a ring spanner on them, I used ordinary dome headed screws for the rest of the cowl
Arwyn