You're welcome.
The difference in the alternator / headlight harness is fairly minor. Basically, the brown wire that comes from the #4 terminal on the voltage regulator gets moved over to what's otherwise an empty cavity on the bulkhead connector. Then a black wire with a white stripe gets added for one leg of the battery gauge (ammeter) circuit. It goes into the bulkhead connector cavity where the brown wire was and runs to the buss bar on the horn relay.
There isn't a whole lot of difference between the warning light vs. gauge style engine harnesses either. The version for gauges doesn't have a dark blue wire for the "oil" light since the oil pressure gauge is mechanical. And the gauge version eliminates the light green wire that used to go to the "cold" light. A black wire takes the place of that light green wire and forms the other leg of the battery gauge circuit. It connects to the large "batt" stud on the starter solenoid. Finally, the dark green wire that used to go to the "hot" light gets re-used for the temp gauge sender and has a different connector to plug onto the gauge style sending unit.
The gauge version of the cab / under-dash harness has a couple of wires re-located on the driver side bulkhead connector to work with the slightly different layout of the gauge style alternator / headlight harness. And has an added black wire with white stripe on that side to complete the connection back to the battery gauge. Over on the passenger side bulkhead connector (that plugs into the engine harness) it lacks the dark blue wire for the oil light. And it has a black wire (instead of light green) for the battery gauge (instead of the "cold" light). Finally, it doesn't have a connection between the dark green wire and ignition switch that was used in the warning light style harness to perform a "bulb check" on the "hot" light.
The change to HEI involves locating the special resistance wire in the engine harness, which typically has a cloth type insulation and runs down to the starter solenoid "R" terminal where it joins up with a yellow wire that runs up to the coil. Once located, you can remove that resistance wire (along with the yellow wire and connection to the R terminal) and replace it with a section of 12ga copper stranded automotive primary wire. You'll need a couple of Packard/Delphi 56 series terminals to crimp onto the wire (a male one for the bulkhead connector end and a female one for the HEI distributor end). And snap a Packard/Delphi #8917644 connector shell on over the female terminal (this plastic connector shell has a latch that will hold it firmly in place on the HEI distributor cap). No changes to the cab / under-dash harness are necessary for HEI since the rest of the run back to the ignition switch already uses regular copper wire.
As for wiring diagrams, I do have a few listed on my '66 Chevy truck gauge conversion page at:
http://rmcavoy.freeshell.org/Truck_gauges.html They're about 3/4 of the way down the page under the heading "Factory Wiring Diagrams". And at the very bottom of the page, I have some links to some simplified diagrams I drew focusing on the differences between the warning light vs. gauge clusters. Those last diagrams are on my photobucket album and they're links, not 3rd party hosted, so they should still be accessible.