The stand alone megasquirt, has an 02 input but its analog. You’ll need something like an LC2 wide band controller with an analog output. Just wired up a customers 92 turbo fox with an MS3 evo. Here is the mounting position of the Megasquirt and Innovate wideband controller in the passenger kick panel where the stock ecu usually is. The O2 wide band will come with the controller. The 02 sensor for this build is in the downpipe. And to answer your question, wide band and narrow band O2’s are the same size. You can use the bungs you already have. Just pick a side and cap the other.