I've recently been delving into the subject and have more questions than answers, so, here are some for starters:

1. When did the large, passenger side, center, valve cover wire harness retention tab begin and end during production?

2. What was the location of the plug wire loom that stands upright on the rear, top, of the drivers side valve cover for 1970 & 1971? If the location varied, how and why, and for what specific applications? Was this exact same cover & loom configuration used on non 340 engines? Was it used during any year beyond 1971?