Wrong Alternator?

I have a 68 Dart that came with a slant six. I put a 340 in it from a 72 Duster. I got a V8 electronic ignition engine harness when I did the switch. My alternator quit charging last year on the way to Carlisle. I got a used one at the show and made it home. I put a new reman in it when I got home and it just stopped charging during the first ride of the year today. How do I know if I am using the correct alternator? The first pic shows the type I have been using.
The second pic shows the type that comes up when I search for a 72 Duster 340. Which one is correct? Thanks FABO.

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