Hi,
the ReadGmsh function in Netgen 6.2 is a pure python function.
Since most function in the python interface are exported c++ function, you might find all necessary functions somewhere in the c++ code. But I wouldn't recommend you to start digging!
Is it feasible for you to use a Netgen 6.2 with python interface for converting and an older version in your code?
Regards,
Christoph