fritz:

Do they also offer the option of an external oil filler cap on the RH rear flank of the car?
Some of the cars appear to have one. 

That was only done on the 1972 model year - the oil tank in the 964 is in the engine compartment.  Weight distribution was better with the forward tank in '72, but too many owners (or fuel station attendants) filled it with fuel heart

Some race cars place the oil tank in the forward trunk, which is even better for weight distribution...

 

16 Cayman GT4, 73 Carrera RS 2.7 Carbon Fiber replica (1,890 lbs), 06 EVO9 with track mods. Former: 73 911S, Two 951S's, 996 C2, 993 C2, 98 Ferrari 550, 79 635CSi