[jambo]

Ideally, what you'd do, is get a standard pipe that hasn't been cut. You might even be able to swap with someone who wanted to fit an after-market exhaust, to save them cutting anything.

Failing that, you have 2 1/2s of a system, you need to make sure you cut the exhausts in such a place that they both have that bit of pipe with them. This probably means cutting your existing pipe exactly where the spare can has been cut.

The lambda sensor is an electronic plug that comes out of the exhaust system somewhere around the place you would like to cut. Have a hunt with a torch, you'll soon see a plug and wire coming out.

The CAT is internal to the link pipe, you'll probably end up cutting through it's honeycomb structure, so make sure the ends are cleaned up so they don't close off too much flow.

Jambo