The <1969 912 (not the 912E) used the 901 style box. This was amended (in the carrera) at the start of the '70s to use a pull-clutch (gearbox is known as a "911") and then this was replaced by the stronger 915 after a couple of years.
So, any <1969 912 should have the push-to-release clutch (same as bug), operated by an arm that exits on the lower left side of the bellhousing (which is pulled towards the front of the car by the clutch pedal cable). This can be operated by the bug clutch cable with some work.
The gear linkage is a custom fit job. You can either replace the shifter and whole linkage with the 911 parts (needs tunnel fabrication to mount, cut-shut the shift rod, etc). Or you can still use a stock bug style shifter and rod but it will still need some work to set up properly (extend and bend or add a couple of UJs / supports). Plenty of info on the web about the linkage set up.
some useful info:
http://www.germanlook.net/forums/showthread.php?t=10575
and even better (useful gearbox id photos etc).
http://www.germanlook.net/forums/showthread.php?t=9153