Worn Timing Chain

I guess I would not even consider not changing the chain, as the chains are also subject to wear in the internal links and will 'stretch' due to that, regardless of what is going on at the contact areas with the gears. In the case in the photos above the gears showed minimal wear on the contact faces, so the chain stretch was likely the main contributor to the 5 degrees or so of cam timing slippage.

In this situation, I first put on the new chain and cam gear with the original crank gear and checked the slack. I then put in the new crank gear and re-checked and the overall slack decreased noticeably with the new crank gear, so the original crank gear either had worn some more than I could detect or was not compatible with the new chain. The shape of both gears' teeth on the Cloyes replacement was different from the original unit, so that might explain it, and it seemed to be inviting more problems to run the new chain with the old crank gear.