I don't particularly like the ammeter idea because it involves running heavy gage main wires from the regulator to the dash & back. These cars have enough problems with shorts, loose connections & burned wires without adding to the problem. If you do use an ammeter, put 50 amp fuses in both wires.
There is the possibility of using a Hall effect transducer in the existing wiring at the voltage regulator & using light gage wires to the actual dash meter, but this gets expensive.
May I suggest a voltmeter instead. A good one will tell you a lot about what is happening. When the"dynamo" is putting out the meter should read around 14 volts at 2000 rpm, with a charged battery. If there is no charging the meter will read around 12 volts. Takes a bit more to learn to interpret the voltmeter but better in my estimation.
D