I had a issue making my 74 Ford Grand Torino pass. 351 Cleveland, with cam, and headers. My solution after talking w/ the smog test guy. No way in hell was that car going to pass. Because of the age, you are given a higher limit of gasses. To what a perfect mantained, optimal running 351 should be running at. I was way above the limit. He was really cool, and let me try to lean it out, adjust my timing. Nothing worked. So after talking to him, he said just put a cat on the bitch. Genius, went home, grabbed my cat off my 3000 GT, cut my exhaust off, the length of the cat, and wedged it in there. Didn't cut the flanges off it or anything, I still needed it for my other car. Just pushed it in, Exhaust leak and all. He put the probe in that side w/ my shoved in cat and it passed w/ flying colors.
So you could allways try to put a cat on it. I live in Las Vegas, so our laws are not as strict as Cali, but the smog guy said that the laws only forbid you from removing, disabling stock emissions, they don't say anything about adding a modern cat. So now my 74 has a flanged end on the left pipe, I had a test pipe made and next test time, all I gotta do is unbolt 4 bolts, replace w/ the cat and make sure the smog guy only tests my left side.