I have 240Z, door and both styles of 280Z doors so if you need any measurements let me know.
I think the only difference between the 280 doors is the location of the door lock pull. To over come this I would design the panels with no door lock pull and mold in reliefs on the inside for each style. Then the buyer can drill the hole where they need it and it won't require two different molds. The 260 and 280 armrests and door pulls have the same mounting holes, but the 240's are different.