1990 Mondial t Cat ECU Questions

Can someone please post the location of the ECU cat along with relevant information regarding the "old style" vs. new style? How do I know I am getting the new style? I think one of mine is old as one has a green face and one black. BUT, I am not sure I know where it is and/or what it looks like. Also, if I am getting a Slow Down 1/4 light that is putting it in limp mode, will swapping the cat ECUs show me if one is bad? Where is the thermocouple?

 

Thanks to all who helped me with my issue. Turned out to be the thermocouple. Thanks again, Daren