Hi Ronos!
I'm a 3SGTE guy, a bit stupid when it comes to the younger siblings of 4AGE, but there a couple of my friends whom actually used the 6-Speed box.
So from what i've heard (yes i actually asked them after u post), there is the C160-12C (with LSD), from a Trueno BZR. and that one have the same ratio as the C60 gearboxes, it made it some how slightly weaker but not significant due to the narrow gear.
While there is the other brother gearbox which is dubbed the C161-G6R, which have a different ratio,
this one might be the stronger one.