What I would suggest is take some patterns of the curvature of the roof and then hit the wreckers yards to find a station wagon or car roof that is close to the patterns. Once you find one that suits rip the whole roof off through the pillars so that you have a reasonably solid structure to handle. With careful marking out then cut the desired piece from the donor to fit into the T Sedan. It sounds real simple when one types it but sadly, it is a big job but a well satisfying job once done.
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