Hunter:
In both my 40B and 155A the cowl panels have a number of retainers. First, there is a "clip" welded to the upper side of the body sill at the bottom of the panel. In front of that, the steel portion of the "slanted" floorboard receiver has a slot formed to accept the angled portion of the side panel. At the upper forward front corner of the panel there is a clip attached to the body which retains that corner of the panel. On the aft verticle side of the panel there are a number of oval slotted sheet metal screws and cup washers that attach the side panel to the front doorpost. You should be able to see the holes in the doorpost for those screws.