ON my '53 pickup with the one wire alternator I hooked the output to the positive connection on the starter where the positive battery cable is. Keep in mind that with an alternator you will now be dealing with volts and not amps so your old gauge won't tell you what you need to know about battery charge.
For the voltage reducer it depends on what you are running on 6V and how much amperage you are converting. If you want to run something that you only use when the ignition is on you have to come off of the switch. If it is something you need when the swats may be off you can connect at any always hot connection. That could be the hot to the switch or the hot from the battery. I needs to be fused. Don't ask how I know this! frown These old ignition switches don't have an accessory position which come into play with any thing you may want on when the engine is not running.


"I wonder if God created man because he was disappointed in the monkey?" Mark Twain