i was in a gb where i was armed with 4 twi pcs and 1 northwind pcs. after the fight, i get the msg that my armor is not enough to get gb rep.
today, i was in another gb where i was armed with 5 twi pcs. i received gb rep after the fight.
so it seems as if the system is not treating the northwind as the equivalent of a twi for gb rep purposes. that would seems to be a bug.