This may be impractical due to variations in the capacitance of the transistors, as it's not a designed feature, so the manufacturers let it be whatever wild value it wants. If you're going to build this in real life, then you should make the resistor a potentiometer if you have one, because the resistor directly controls the frequency. A 3.3MOhm Resistor gives it a frequency of 600KHz, potentially useful for a coiless AM radio transmitter (like @thebugger's one), and a 560ohm resistor gives a highly unrealistic frequency of 1GHz. If you are going to use this for an AM radio transmitter, then it should be no more than a prototype, because I imagine that it would be very unstable in frequency.
