It should the square connector one like this. I wonder if you removed the right one, check the neighboring ones to see if there's a squarish connector one (-that is right one)...
97 80 Series Y-Pipe with 1st stage Catalytic converter, replaced at 168k mile
Very good conditions, just need to extract one severed bolt out of the O2 mount
$400 + shipping
Located in San Francisco Bay area.