The 65 valve covers didn't have the small slot between each pair of plug wire holders that were built in to the finned valve cover caps, as you can see on the OP's valve covers (at least on the left side
, I can't quite make out the right side). That's because the 65 wires had individual nylon thingies around the wire that sat in the valve cover bracket.
The later ones used a nylon thingie that was two wires wide and snapped into the valve cover, like below. That's what the little slot on the later valve covers is for.
