You need 9.5 volts to charge an 8 volt battery; your generator puts out 7.5 volts to charge the 6 volt battery. Trying to charge an 8 volt battery with 7.5 volts gets you a perpetually discharged 8 volt battery operating at about 50% capacity. Trying to charge it with a 12v charger gets you a boiled battery. Adjusting the 8N voltage regulator to put out 9.5 volts requires special tools and expertise to do it correctly. Or, you can try it yourself as long as you are prepared for the consequences of failure: a boiled battery, a burned up v/r or no charge at all. Cranking up the output on a 2 or 9N generator will increase the charging voltage but at the cost of overheating the generator. Having a partially discharged 8 volt battery in your tractor is no better than having a fully charged 6 volt battery. At 8.43 volts, your 8v battery is fully charged. And it needed 9.4 volts to get there. But, at 8.04 volts, your 8v battery is only 25% charged. In other words, it’s no better than a 6v battery at that point. If you already have an 8v battery and the v/r was adjusted to put out 9.5 volts, chances are very good that it is no longer doing that. Because the adjustment was made by bending the points arm. Is that how ignition points are adjusted? You will also need to keep checking your voltage output every few months because it will change with both time and temperature. Remember, it’s only about 2 volts that makes the difference between no charge and a boiled battery.
IMHO…….cleaning up the grounds, replacing the cables and buying a new 6v battery is a lot easier.