While I do not have a 67 Chevelle wiring diagram, below is how I would modify a 67 Nova setup.
First, this is how things were from the factory with just the main feed from the battery going through fusible links and then to things like the factory alternator, external voltage regulator, horn relay buss, more fusible links, and then the feed to and through the firewall bulkhead connector and then the feeds to the fuse block, headlights, and ignition switch:
Same as above but just condensed some so one can see things better:
Now the original feed wire from the junction block by the battery going to the alternator output post, the original external voltage regulator, and the horn relay buss is removed:
Now a new 10 gauge wire needs to be run from the junction block by the battery to the horn relay buss. Notice too that I have kept in place the fusible link between the junction block by the battery and the one end of the new 10 gauge wire for protection as well as leaving the next fusible link off of the horn relay buss going to a smaller gauge wire that then goes to and through the bulkhead connector:
NOW, I then remove the original ground cable and wire from the battery negative post to the engine block and the back of the radiator support:
Next, one would put in new 4 gauge wire from the output post of the new alternator as well as adding a new 4 gauge from the alternator case and then these two cables would go to the respective battery posts. Also from the negative battery post a new 4 gauge wire would be run to the body of the car:
Now to add your added accessories such as an electric fuel, electric cooling fans, air ride compressors, audio amplifiers,and such these would then get main power from the battery and going through the proper wire protection device:
Hope this helps.