This will be a challenge, too. The harness you have isn't wired for the four pole ignition switch on the headlight, it doesn't have indicators, and your switches are a different configuration.
What kind of indicators were you planning to use?
I think the closest one made is this German one. But it's a battery model.
It has the indicators on the headset, and the ignition switch.
The handle bar switches are different, though. It has the add-on turn signal on the left side, and yours has the two square switches.
The German version
Your American 1975
The switches on your handlebars.
I believe the harness you have has one switch that's high/low beam, horn, kill, and lights on/off.