Q201 , Q202 in the power supply should be OK to use silicon transistors. Depending on the transitor gain one may want to change the frequency adjust trimmer a little, e.g. to allow a higher resistance if the transistors have more gain.
Q113, Q114, Q203, Q204 are a bit more tricky. These are used as chopper demodulation and may need high low CE saturation and maybe higher BE reverse voltage.
edit: The MPS404 looks like a special chopper transistor, maybe OK for Q113 and so on. For Q201, Q202 it could be more normal ones, maybe a little higher current ones like BC636.