Unless there was some kind of modification, your basic 89 with a 302 setup, runs with a single cat. You have a crossover pipe from the left bank (that runs under the motor & trans), It ties into the right bank exhaust for an oxygen sensor, then two pipes run into one cat & combine... After the cat you have a resonator, then muffler and tail pipe.
If you want to eliminate your cat and go a true duel exhaust (if it's legal to do)... i would think you still would want to run the left bank exhaust like normal with the crossover pipe under the engine & trans and tie into the right bank exhaust... You wouldn't need to come into a "Y", but you would have to attach the two pipes so you can keep one oxygen sensor to measure both banks of exhaust, then just run straight pipes out to a muffler of your choosing.
Anyways that is my best guess.
In theory if you have a strong low mileage motor. You could just run one O2 sensor to either side of the exhaust, because your computer will take reads from that and adjust both engine banks to compensate anyway... I wouldn't of course recommend it, i personally would rather have both bank exhaust O2 reading but as in theory it could be done that way.
If i remember correctly there was an aftermarket kit for this (I don't remember the name of it), that you could split the exhaust into true duel exhaust and run two O2 sensors (one for each bank) and it would go into this do-hicky (LOL) and combine the reading to fool your computer... I'm sorry about being vague about it but it's been at least 15 years since i seen that kit & it's getting late... It might not be necessary anymore with these newer style O2 sensors....
Somebody I'm sure will speak up who knows more about this.
Good luck
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