David,
Try to find a local artisan to create the cladding for the doors, which I am sure are a custom size anyway. The substrate material should be durable and rot resistant, such as cedar. I was confronted with a similar issue several years ago in NJ, when I had to replace a pair of historic doors with a fire egress door. I found a local artisan who carved a single door that mimicked the original pair using Spanish cedar. Good Luck!
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David Singer AIA
Principal
David B. Singer AIA Architect
Stockton NJ
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