Im building a sohc turbo. I have an air fuel gauge for it but i read without a wideband O2 sensor its just a light show.

So where is a place that sells it for ek's?
I google and didnt find anything solid.

Also read that the K seriesO2 sensor is a stock wideband. Could those be used on ek's as well?

 

look on eBay for Bosch LSU, they are $50 new. If the K series uses a wide band, that may work. I believe the Civic HX in the EK had a stock wide band.

As the sensors are used, they very gradually become lazier and they won't appear worn out until they are very very worn out. Basically, spend a few bucks more to get a new sensor to protect your expensive investment. No reason to cheap out on engine management.