Most likely a 67-72 A-body centerlink. Same for /6 and V/8. That bolt through idler is 68-72 if its for an A-body. 64-66 and 67 idlers had a stud in them that went into the K-member.
There is no such thing as a /6 only or V/8 only centerlink for a 67 or newer A-body.
But, it could be a 64-66 A-body centerlink. Those came in /6 and V/8 versions. The length is different than the later ones. I don't know the measurements.