I really don't think the MAF is the issue. ECUs are quite smart at self diagnosis these days. If it's saying it's a lean trim (too much air) post cat, then it's likely getting the correct voltage from the MAF.
The most likely introduction of air would be either the joint between the headers and the cats, likely a poorly positioned or altogether missing gasket; OR a crack in the weld. When I got those codes it was a crack in the weld. Super easy fix. Hard to detect, though, due to the crack developing on the edge of the weld puddle which was able to hide it from being visible but I could feel and hear the wind coming out of it when the car was idling above me.
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35% Hooper Optik | Takeda Attack CAI | F.I. HFC | Hotchkis Sway Bar | Stillen 24row | OS Giken Super Lock LSD | TK Shift Knob | EVO-R Carbon Diffuser
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