The way we are making the Series I/II pickups now, we match them as a set of three. I suppose you could start with just replacing the single coils, but you won't get the best high frequency cancellation with the original humcanceller. You'll find the result much better if you replace all three.
We have used an industrial super glue most of the time. Some people that worked here tried different adhesives over the years, including epoxy (!). If a rubber mallet strike doesn't easily dislodge the humcenceller, then the screw technique or router as Jimmy suggested will be needed.
