for clarification.
Clock source is pierce oscillator with one inverter from 74HC04 and other (5) inverter parallel is used as power driver of the circuits on the schematic that is, they are connected to L2. 74HC04 is powered 5.8V. 20mA was meant as max output current for 5.5V, not as output current into this load.
schematic with IRF510 in the picture is first amplification phase in two transistor amplifer and it only wakes the power output transistor. Actually works by 25Ohm 6W resistor parallel with Ciss output MOSFET about 1900pF. Yes. transistor Q2 not works with +12V , but with +24V on L1 is in real DC +24V.
However, I still do not know how to calculate the size of L2 and whether Cis C resonant or just define the resistance to charge C? Yes i saw similar wiring where instead of L2 was 5-10W Ohmic resistor, but her is relatively expensive toroids inductor and it must have a reason and somehow it has to go to calculate its value.