The 120k
resistor is for regenerative feedback between the Q2 NPN transistor and the input to the tank circuit. The value of this resistor is important to the performance of the entire AM receiver.
In fact, it may be better to replace the fixed value with a variable resistor paired with a fixed resistor to adjust the oscillation and sensitivity. All the connections should be short to minimize interference.
Performance will vary depending on stray capacitance in your layout, the inductor winding/core/length, etc. Changing values of some of the capacitors, or adding them, as well as a potentiometer in the feedback loop can help with the performance of the receiver.
With such a small circuit that is affected so much by its construction and its environment, a lot of hand tuning and experimentation will be fun, instructive, and possibly necessary to make it work best.