You might get a better response in the TECH HELP thread.
Or try a search there.

But I don't understand why the cat's have been replaced many times. My 88 is still sportin the original cats with 109K on the clock. New Jersey isn't CA, but we have probably above average emission requirements. I never have any problems. If you neighbor is blowing thru Cats, he's got some other problems.

Good luck to your friend.