C1 and C2 are just DC block capacitors. L1, C3 and L2 is a pi network filter that provides just the right amount of phase shift to make the oscillater oscillate at the "desired" frequency. Basically it's a form of Hartley oscillator and relies on the oscillator output having some amount of internal resistance as well: -
It could quite easily be re-configured to use a Colpitts confuguration of Pi network (two capacitors and one inductor): -
So there is a phase shift of several tens of degrees brought about by the internal driver resistance and one of the inductors and this will be added to the phase shift of the 4.7 pF and the other inductor. The LC phase shift is nominally 90 degrees at perfect resonance but it will likely run slightly off resonance (a phase shift greater than 90 degrees) so that the total phase shift is 180 degrees. Therefore it is highly likely that the circuit internal to the oscillator is just an inverting stage.
C1 and C2 can change value but there will be a small change in oscillator frequency. However, given that the oscillator appears to be a VCO (hence the pins marked VCOA and VCOB) I don't think this will be a big deal.