So I have a trunk divider from a 66 Belvedere (old part) and my reproduction based off 3 samples from 69/70 B bodies.

Basically the same.

Are the back seats on the 66-70 cars the same? I looked on AMD's website for the rear floor pan and it says
"Rear Floor / Under Rear Seat Pan - 68-70 Dodge Plymouth B-Body (Modification for 66-67 Models: Seat belts mount differently on 66-67 models and will require modification.)

Funny thing is there are NO good pictures and even worse info online. Just have to laugh. Most companies list the same trunk divider fitting 67-69 Barracuda and E bodies! Those are completely different.