Sounds like a fun project. I will never forget the 68 stepside I took 9 years to build
The file I attached if offered by one of the very popular e-fan harness sellers. The rest of the tune is not useful. I would just copy over the fan information from it. But raise the fan disable speed to 25 mph or so.
Also, does your harness have 2 or 3 relays to control fans? The 2 relay systems control the fans separately. The 3 relay systems control them together allowing both at low speed (though fan #1) and both at high speed (through fan #2).