internal/external & nuetral balance flywheels

I need some clarification on a few points about flywheels.
#1 is ... is the flywheel for internal balanced engine the same as nuetral balanced?

#2 I know 360's are external balanced how much does the harmonic balancer contribute to the balance?

#3 on a 318 is it nuetral balanced flywheel or being internal balanced motor does it still have a balancing effect on the motor? (i have seen them with drillings on the back )

thanks