That's a lot of revs BUT 6v filaments can take a bit of lighting up if hooked up directly, esp if using a h/lamp bulb of some power.
If you preheat the bulb off a battery and then hook it on when warm it will tell you a bit more. I would expect to see light coming on under 2000rpm and brightening with more revs until it could well blow - but I would get a meter across d & f to Earth first to see that you are getting a steady increase in volts, no load on, from around 1000rpm, building to maybe 20v with a burst of speed. Then hook loads on to see if it supports eg 45 watts and still is showing over 7v on the meter around the 2000 mark. 12v bulbs are easier for this, and less likely to blow due to lack of regulation while doing crude checks.
Better still, get a battery and working regulator hooked on and measure the voltage from A on reg, or across battery, with loads switched on. If the dynamo and reg are any good the system should show a steady 7+ a bit voltage at medium revs with all loads switched on. The system, on the bike, should be regulating steadily by about 2000 engine, maybe 2500 dynamo, with steady lights and steadyish battery voltage depending on vagaries of meter being used. You would also be able to observe the cutout working, especially if you DISconnect the battery while measuring voltage coming out of A.
