A 302 will run for a looooooong time. I've had a few of those engines myself. On at least one of them, the chains were a bit slack and close enough to the tolerance limit that I replaced them. Keep in mind they have no tensioners or adjusters for the old 302 I was working on.
The Contique engine, on the other hand, has tensioners for the OHC system that keep slack out of the picture under normal conditions. That's your difference. If the chains get a bit worn or stretched, the tensioners just take up the slack.
At 200k miles (or even earlier) you may want to change the chains & tensioner system if they show any obvious signs of extreme wear, but in a properly maintained engine, that may not be needed even at that mileage.
