Re: inductive reactance!
The choke is used to filter out the 100MHz content in the power supply to the low frequency amplifier T1/T2.
To make a filter, you need always at least two impedances, here the choke together with R8 is the first one, C4 is the second one.
The value of the choke needed depends on how much you need to decrease the 100Mc ripple on the power supply.
For example, if you need -60dB (1000 times less on the LF side than on the HF side), Zc/((Zl+R8)+Zc) must be 1/1000. (Zc is the impedance of the capacitor, Lc is the impedance of the choke, google for the formulas if needed).
Be sure you use a capacitor that has not too much parasitic behavior on 100MC.
Stefaan