Checked your timing gear?

Idling engines and stick shift engines are harder on chains, and a 360 being harder on a chain than a 318, would be impossible, there is no difference on cam gear....... remember, anything but a low idle the chain isn't slapping back and forth, the valvetrain overides the inertia of the camshaft and sprocket, so the chain is always on a tension, four speeds and low idling engines would cause a bit of slap, with the herky jerky from the clutch.

The older engines with the hollow cam cover bolt and deflector seem to have the chains last the longest, as long as they aren't nylon........

high paraffin oils also seem to collect of the chain, cutting iff the oil to the joints, because the chain runs cooler.

I put 110,000 on a cloyes double roller chain, sure, it stretched, but I saved it for re-use, it wasn't that bad, that chian spent he first 10K pulling a solid roller 590/610 lift cam too.