While there are opinions on how big your ground wires need to be, it could vary on your routing on what you need to properly ground sh*t.
TYPICALLY- and I use that term lightly- your main concern #1 should be ensure whatever size battery cable you use, both positive and negative needs to be the same size. Most people say for fuel lines, bigger is better, and I'll add to that the size of battery cables, IMO. This also goes for power and ground wires to any electrical component. If you use a 14 ga. power wire to your stereo, you should also use a 14 ga or larger ground wire. For the life of me if you've ever seen most factory G-body pos/neg cables, you may mistake them for radio wires. I exaggerate to clarify. Those are some TINY cables. Yet they seem to work. Electrical engineers are smarter than me. All I know is that if I were doing mods, larger battery cables could not hurt.
It appears that you're already set with your battery cables and are looking for accessory grounds. ECMs, alternators, compressor clutches and sensors and other electronic junk could cause an electrical imbalance and those engine to firewall woven straps carry more amps than their size lets on due to their construction as well as being more flexible than a sheathed cable. Don't need much. I've heard of some people using a ground strap on both heads to the firewall but usually when the negative battery cable is attached to the frame. For my own experience, Oldsmobile V8s used negative battery cable to the driver side head all day long.
Regardless of whatever grounding stuff you use, the key is METAL TO METAL contact points. Don't rely on screw/bolt threads alone unless it's like a welded stud or something. Get rid of paint, sealer or anything else that can stop a metal to metal contact. Then you can touch up paint over that, or smear a little sealer goo over it like the factory and protect the area after you get good ground.
