I had to re -seal the rear window on my 403 a couple of years ago. I bonded
the glass in place with a modern glass adhesive. As you will know, modern
car screens are secured this way. This glass will not require holding in
place whilst it sets as it has very good 'grab' qualities, and it will not
leak. An inner frame is required to fix the headlining to, and to hold the
aluminium trim. I made this up from strips of Millboard. This is a very
dense cardboard type of material which is used for glove boxes etc. and can
be built up to the required thickness using Evostik or similar between
layers. You can use the 'inner' suface of the alluminium trim to wrap the
board around, to give the correct shape, and keep adding layers until the
correct thickness is achieved. It can be trimmed as necessary with a sharp
blade when the glue is dry and then screw into place in the same way as the
original timber, and is hard enough to hold staples to secure the
headlining.
I hope this is helpful.
Mike.