4.1.- My bike is a Honda Africa Twin from 2000, and it does not have fork oil release bolt in low side of the bottle, Is...
... it necessary to take out 120 c.c. as indicated in the instructions?
Yes, it is strictly necessary.
An alternative method to take out 120 c.c. is by aspirating that volume using a big size syringe connected to a plastic tube.
This alternative method can be used when you do know that oil volume in the fork is the one determined by the manufacturer.