'94 SE 4x4 exhaust issue/failing smog

[devin]

My '94 has TWO (2) catalytic converters. I realize most people will think I'm wrong about this, no specs I've come across mention 2 converters and every parts store employee I've questioned has dismissed me as an idiot. But it's true (verified by a certified Nissan mechanic's visual inspection) and I'm now in need of a replacement for the 1st converter in line from the Y connector pipe. I already replaced the second in line with a $160 Magna Flow converter (O'Reilly Auto Parts part #39004). Who can tell me what part will work for this smaller (approx 2/3 size of 2nd)unit. Any help would be appreciated. Thx in advance!