If in NSW this engine must be run with a cat. The rules changed 2 and a bit years ago. I was unable to engineer my 73 model Corolla without one. Pointless asking the question here. Run all of your questions by the consulting engineer that you plan to check the car and then have him do it. At the end of the day it is his interpretation of the rules that matters, no-one elses. Regards YelloRolla