Window regulator variants...

I have recently discovered that there are at least 3 types of window regulators for the 70-76 A-bodies. I thought for some reason that 70-72 were all the same and that in 73 they went to the post type regulator. After purchasing a drivers window for my 75 Duster from a guy in CO it turms out it must have been from a 73? It won't fit my early door or the 75..... Anyone have the scoop on this?

BD