FiTech EFI system

For the people not running headers, where would the ideal location be on the o2 sensor? Close to the manifolds on the vertical run of the pipe or farther down to the horizontal run of the exhaust?
And on another note.. if the dist was originally ran through a coolant temp vacuum switch, should that be bypassed or run in series with the switch. This is on the base model fitech that does not control timing.