I had real trouble finding a suitable alternative oxygen/lambda probe for my 1992 Rev 2 MR2 Turbo. I can’t find the original Denso part number at the moment, but I managed to find that a Denso DOX-0107 fits the flange size correctly and is 1-wire, it just requires soldering to the original connector. It’s got a Flange 44 type flange which apparently matches the 3SGTE.
I got it from http://service-parts.co.uk/denso-oxygen-sensor-dox-0107
I received an Innovate Wideband lambda/oxygen/AFR gauge for Christmas and decided to get it installed on my ’87 classic Mini today. Last year I fitted a new stainless exhaust system with a stainless Maniflow LCB 3-2-1 exhaust header, stainless centre silencer and RC40 millennium twin centre exit DTM back box. The lambda sensor requires fitting a threaded boss into the exhaust. The exaust system has a Y piece where the headers join to the centre pipe, and this is th most appropriate place for a lambda sensor as it measures all cylinders.