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.
Here’s some pictures of some minis I liked: http://www.flickr.com/photos/gadgit/sets/72157633883355053/