Lambda Sensor Placement

[eliotmansfield]

Hi,
Ive purchased a 4 wire heater Lambda[Oxygen] sensor to enable me to calibrate my edelbrock carb on my 350sbc accurately.
Ive got a 8 into 2 into 1 exhaust system, and i cant decide where to place the sensor.
Either on the single 3" part -or- on one (or both sides) immediatley after the collectors.

Here's a picture of my pipe:
www.mez.co.uk/dcam/05120006.JPG

Any thoughts welcome..

Eliot,