Our first 240 was a '76--no cat--front pipe ran back to the muffler. I think '78 was the first year for a cat - at least here in NY--CA had them first earlier.
I may have a $ saving path for you--at least as far as the "kit" goes. I had a client who I guided through 2 years of 240 ownership but his mom recently gave him her fairly late model Civic. The 240 is now off the road. Before that he had purchased a "kit". When he changed to the Civic he called to see if I was interested in taking the kit off his hands. I had no need for it at the time. When I checked where you live I thought of Tim immediately (he's in Babylon Village). I called him - he still has it--wants $100. You can reach him at six-three-one-316-3892. He's a nice hardworking young fellow and I'm happy to help him out. -- Dave