Emergency brake question

I just got my 70 Duster. The emergency brake assy is completly gone. I need one to pass my state safety inspection. I figured the parts needed would be the same from say 67 to 76 but looking on Ebay I see parts for 73 to 76 model Dusters and Darts are listed seperately......what changed on the emergency brake starting in 73 that would prevent it from being used on a 70? Thanks in advance for any help.
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