If I had to take a stab at it I'd likely cut the extended cab a little forward of the rear door. Almost all the way up to the windshield. Chop the crew cab roof and floor/rocker about middle of the back door. Allows the latches for the 3rd door to still be used and the Nader pin of the third door and the ext cab portion to engage the rear door latches of the rear crew doors. I'd also be doing a fair bit of bracing for rollover protection as well as strength for the extended frame.Looks more like they grafted the back half of an extended cab to a crew cab. Then like daly said figured out how to make an extended cab 3rd door work with the rear crew door.
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