My thanks to Peter Clukey at Lockheed Martin for providing the definitive answer:
It is a Type 308 transmitting antenna for a Rebecca (BABS) homing system. The 649/749 Constellation parts catalog lists the two stub antennas on the nose protrusion as being two separate units, one being a Type 308 Transmitter and the other being a Type 15 Director. See items 42 and 43 on the following diagram.
The receiving antenna can be seen under the name "Smith" in this image. This type of antenna was common to many other types.
Thanks to all who contributed.