Wilson twin 20 amp

Way back around 1972 I picked up a copy of The Audio Armature. Back then they referred to an an amplifier project from a few years earlier called the Wilson Twin 20 at least I think that was the name. Does anyone here have the schematic of that amp ?
 
I'm scratching my head about the following:
1 - What were/are the active devices?
2 - TR4's emitter relates, together with TR6's collector, to R15. Does this really replace the Baxandall diode and resistor almost commonly found in quasicomp output stages?
Best regards!