You are close.
1975. I’ve parted out a few A body cars. The ‘75 models first got the converters and a different floorpan with a bulge to allow clearance around it.
Was it a mid-year change in ‘75? I knew the ‘76 models had it but I haven’t seen a ton of ‘75’s. I seem to recall hearing not all the ‘75’s had it but clearly there’s some bad information floating around.
