A genuine GPO 205 rectifier (style varies) and a 3.3K ohm resistor for all GPO 700 series telephone conversions. The rectifier is a used item, the resistor is new. The 205 rectifier element is designed to prevent acoustic shock. It connects between the T1 and T2 terminals and should be fitted wherever the rectifier is not present. The rectifier diode element is not polarity sensitive, so can be fitted either way across the two terminals.
The style and colour of 205 rectifiers supplied by the GPO and BT varied greatly, all rectifiers sold are selected at random.