I would try an 2n3055, they are easily found, you have 2N3772, 2N5686, 2N6338, 2N6339, 2N6340, 2N6341 ... any TO-3 case NPN who has 20 amps collector current.
You have an 4 amp fuse in the line, it would help start the radio.
Do you have an beefy 13.8v 20 amps power supply around, fixed or variable current limited just in case
you could try to put an supply on p4 pin 1 (DCI) once p5 is removed.
Q2 is not necessarily broken, it is an powerful transistor, 100v at 30 amps, normally they wont go up easily, unless a thermal breakdown, badly dissipated heat ... killed it.
You have Q1 and Q3 to check, all the zenners, electrolytics ... low values ceramic or mica capacitors.
The 2 zenners in serial give 10.2 volts (5.1v each)
All this circuit to make an 13.8v regulator ... no current limitation.