An extremely easy lesson :-)
Clean the extreme end of the 8 volt regulator with steel wool or scatch it with a small screwdriver.
Bend the middle of the center pin down at a right angle. Bend the pin again so that the lead is in-line with the back of the metal tab.
Position the regulator as in the picture - just above the audio amp. Solder the regulator to the copper board at both the TAB and the center pin.
Run a wire from the lower pin to the plus side of C9, the 1000uF cap.
Connect a spare 100 nF cap from the top pin (8V OUT) to ground. You may want to use a terminal strip as a distribution point for the 8 volts.
Connect all 8 and 12 volt connections.
12V to U5 pin#1 & #2
12v to U4 pin# 8
8V to R48/Q8
8V to R15/C20
8V to R7 and R6 and R5
This completes the 8V regulator.