I have 2 Alnico 8 magnets on order. plan on making a custom 8 and JB8. This will be my first time magnet swapping. I already praticed removing a magnet from a gabage pickup so im good with that, my question is about putting the new magnet in. I have read on projectguitar.com the magnet has to go in "N" facing the slug bobbins, Will the magnets come already labeled? I also read about checking the magnet with a polarity tester, do i need this? Any info? I want to do this correct.