Anyone know differences between early and late door panels???

[1975stepside]

I've got a '75 C10, very base model truck, no headliner etc. I think the door panels were the same on C10's until around 1977, and then got different somehow. I know my door panels don't have any kind of carpet bit at the bottom, or any kind of elastic pouch, and the arm rests are much thicker than the later ones have. But trying to find decent ones the age of my truck is pretty much not happening, so I'm thinking of using later ones, just need to know what the differences are and if they will work on my '75, or how to make 'em work on it. Can you help? Also, - what years will work? I've seen Blazer door panels up into the early 1990's that look very similar.Thanks!