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You will need all of the power supply components including the filament regulator since the power supply is common to both channels. This is C1 through C7, R1 through R7, R30 and R35, D1 through D5, U1, and an octal socket.
You will need the components to populate one channel of the PC board. R8 through R18, R31 and R34, C8 through C10, Q1, U2, a 9 pin socket and a 4 pin socket.
The resistor that drops the filament voltage for the 5842's (R3) will need to be a higher value since there is only one tube (half the current) the actual resistance value depends on how much voltage vour filament winding puts out.
Depending on your choice of power transformer, R6 may need to be a higher value since there will only be one PowerDrive circuit. The negative voltage will be higher because only half of the current is being drawn leading to too much dissipation in the mosfet. This is probably not required for a 540 VCT transformer used for 45 tubes but will be needed for a 600 VCT or higher transformer used for 300B tubes.