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Those headers and cats on a VE-VF take about 1 1/2 hours. Very easy to do. Don't separate the headers and cats, unbolt the cat back and let it hang off the mounts, disconnect the O2 sensors, undo the steering coupling and move the shaft over to the right, then undo the header bolts and drop them out from the bottom. Fitting is the reverse. Use a thin smear of sensor safe sealant on the old gaskets and bolt them up.