FD3Smaniac

iTrader: (3)

will a regualr TII o2 sensor work in an efini TII engine?

Sideways7

iTrader: (7)

What makes you think you have an efini engine? Technically, the efini was an FD model, and the Infini was the FC. And the main difference was a slightly revised intake and exhaust.
And to answer the question, any O2 sensor from an fc will work.

NZConvertible

There's no such thing as an Efini TII. Assuming you mean Infini, there's no such thing as an Infini engine either. The only power-related mechanical change to the Infini was the exhaust (not intake).

Any generic one-wire O2 sensor will work. You don't need one off or for an FC.