interesting dilemma you have.
I cannot see how the shade could have cracked though. It is aluminum surrounded with a "not so hot' vinyl extrusion. I know mine are often a pain in the arse to slide easily. I'd think the easiest fix is to replace the shade itself.
I doubt the extrusions for the handle edge and the wrap around and very doubtful the closeout itself (inner frame behind ceiling) is still to be had cept from salvage.Inland Andy would know.
A closeout (decorative trim return) that transitioned neatly from the inner ceiling cut to the "smaller" Vista-View surround would be a monumental fabrication challenge IMHO.
The frame of the device is known as the Vista-View Close Out. And as mentioned it is riveted thru outer skin from roof.
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According to 1974 Service Manual here is the removal procedure:
1) Remove Drape
2) Remove Roof Lockers and or panels to permit inside skin to be loosened approximately six feet aft of Vista View in question.
CARE MUST BE TAKEN HERE TO PREVENT METAL (Ceiling) FROM BUCKLING
3) Vista-View closeout frame is held ONLY at top by several hard rivets through roof.Remove these from the outside.
4) Carefully Hold Out Ceiling skin panel and slide Vista-View frame out toward floor. Shade will come out with closeout frame.
- For shade only removal, drill out pop rivets attaching ceiling panel Approximately 2 feet aft of Vista-view window. Hold out ceiling panel skin and slide shade out.
Use #30 bit for rivet removal.
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BTW the illustration shows the ceiling panel skin pulled out both fore and aft of the window in question. Maybe they meant 3 ft either side. Also on most that I have seen there are no overhead lockers in the way of the Vista-Views.
Good Luck
Please advise as to your doings.