Ok folks, here's where I am at:

The grounding wire running from the battery is connected to a plate, which is connected to the bolt at the shock tower as Aaroncake specified here: http://aaroncake.net/RX-7/grounding.htm. The bolt is still in decent condition, so it can be reused. It is not running to the starter though (I'll deal with that at a later time).

The wire continues on to the bolt connecting to the tranny on the driver's side as this thread specified: https://www.rx7club.com/2nd-gen-archive-72/super-grounding-256429/

The cabling is in good condition, however it did have residue from oil on the wiring. I have since sprayed electric cleaner on those connections, and they appear to be clean now, with no residue evident. (I am letting it sit for the time being.)

So, here is my question:

If I pack both exposed spots with the dielectric grease, and cover those wires with electrical tape, will that be effective, or do I need to get new cabling?

 

as long as the cable is still good, the dielectric grease and electrocal tape so be good enough. just make sure any exposed areas get a good connection

 

As long as there is no corrosion, you are fine. Check the cable to make sure that the nasties have not wicked up the wires and eaten away at them under the insulation.

For what it's worth, it really doesn't matter where you put the "starter" ground on the engine. As long as there is a big ground to the engine for the starter then everyone will be happy.