The TB balance adjustment on W5AM bikes is stupidly simple.
Close both air bleeds after the engine is warm. Hold the revs at 3,500-4000 rpm and balance the TB's using the flat bladed screwdriver screw on the bell crank linkage on the LH TB.
Drop the throttle and turn off the engine with the kill switch.
Using Guzzidiag or similar re-set the TPS.
Fire the motor up again, let it idle and whichever side has a higher manifold depression open the air bleed on that TB until they are balanced at idle.
If they are balanced at idle then there is no need to open an air bleed.
The reason your mate's Breva uses both air bleed screws is because the Breva doesn't use a stepper motor to control the idle. With them, although the balancing sequence is identical at the end you increase or decrease the idle speed by adjusting both air bleeds an equal amount.