Ummm I think you need a Lambda sensor, on the K10 Super S there is one of these positioned on the Exhaust manufold I believe (I might be wrong lol), but I dont know how this would be wired up exactly.
Haynes recommend you drill into the downpipe halfway to the CAT, if you have one, and weld the nut on the hole and then put a new lambda sensor in, this is because OEM sensors aren't too reliable.
Davey im in SW london as well... Could we wire the A/F clock under the bonnet so to speak to see if my sensor works, then if all good ill buy it off you (as long as the price is right)