Some of the AFR systems can produce a simulated narrow band output to use as the lambda input into your ecu. I have never personally done this, as I would always advise the use of a proper narrow band sensor for the purpose of running at stoich simply because that is exactly what it was designed for!

However, I only recommend running in closed loop mode for either std or 803 injectored cars and those on mild cams.

The YB engine runs fairly poorly at lambda 1 when using large (i.e 1000cc) injectors and lairy cams.

Personally I never run a tuned YB in closed loop running unless the owner absolutely insists on it, or the car is fitted with a Cat.