Pretty sure I've seen GA motors with only one pulley too, just running an alternator & waterpump.
Aren't most nissan motors supposed to be internally balanced, so there should be no issues with harmonic inbalance?
I don't know if the RS5F41A used in the K10 with the MA motors has the same bell housing as the CG in the K11.
The CG & GA have the same bell housing so any combination of those will bolt up.
From all accounts a CG13 will quickly wear / break the clutch & RS5F41A used with the CG10. A GA will be even more of a problem.