Usually the fluid leaks out in one of two places, the slave cylinder on the bell housing, and the master. You can't see the leak on the master because the end of pokes onto the car and the leaking fluid gets soaked up by the padding under the dash. Only other places it can leak is the metal pipe or the hose umlikely, not impossible.

Getting the hydraulics working should be enough to get the car mobile, unless there was something wrong with the clutch or gearbox.

The overdrive is indeed electric. Well actually it is hydraulic/mechanical, activated by a solenoid. If your car has it it is a large aluminium lump on the end of the gearbox. On a '67 it should be activated by the stalk on the right hand side of the steering column.

Regards