None of the early gearboxes (up to the end of R30 production) have any (usable) identifying marks on the outside. The top of the bellhousing just behind the head sometimes has some stamped numbers/letters which might be a serial number, but only Nissan know
Actually the otherway around - warner on 1-4 and servo on 5th, although have seen one or two with warner synchro on 5th. Only 240Z/260Z 5-speeds got servo synchros on gears 1 to 4
240K 5-speeds used the FS5W71B gearbox, but early cars were 4-speed (FS4W71A) and 3.5 diff ratio.
240Z/260Z used steel front cover, same as 240K. Early 240Z used FS5C71A g/box (flange output; similar to Fairlady gearbox) , late had FS5C71B same as 260Z.