"Mid 60s baracuda 8 1/4"

I have a 70 Dart Swinger with the usual 7 1/4. I have an opportunity to buy an 8 1/4 from a guy who's telling me it came out of a mid 60s fish. For it to bolt up in my Dart it has to be from a second gen (67-69) barracuda right? Just trying to seperate fact from fiction.