Mine is an early (January 31) Dearborn car, but the tab is under the middle Valve Cover bolt.
The rubber "covers" (I assume you are talking about the 90 degree connectors), are not available separately (unless you are a harness builder) as they are molded to the wires. Also, I believe the end (or "ends", depending on which harness you have) were black and not brown. Possibly yours has faded ?
A word of caution in purchasing a repo harness; make sure that all end connectors, and colors of connectors are correct, and match you original. For example, on my '67, which is also a C Code, and without the in dash tach, it had the red connector at the firewall, and the push on spade connector for the oil pressure sending unit, as opposed to the 90 degree push on connector for the post type sending unit. NPD shows this correct harness for 289 with tach. They have also added "or with red connector at firewall". Just be sure that everything matches yours before purchasing.
Bob