Outer Limits 4x4 Board

Does anyone know how to identify the early and late model nissan gearbox? Apparently the early GQ gearboxs had single synchro rings and the later model ones have dual synchro rings. I have spoken to nissan in Townsville and they have suggested pulling apart the gearboxes as they think it may have been 91 or 94 that the dual rings were introduced. Has anyone got any information on the change over date or how to tell the difference without going to the wreckers and stripping a box? (I'm sure they would approve of you stripping a box before you buy it. )

Dual synchros on 2nd and 3rd gear from 94 i think, not 100% sure though. sorry don't know how to tell the difference though

the transfer case will have dextron atf fluid in it instead of gear oil from the change onward. first gear is higher also in later model