Here's some details about how I magnetized the Meganobz box. I think I covered every option, including magnetizing the head on the Big Mek so that he can be a Meganob. The kit makes it easy to swap the hands without magents. There is a peg on the arm that push fits into the fist, and you can make all the Killsaws, power klaws and combi-weapons without duplicating parts. This is great since GW has a bad habit of using the same part in two options (to save space on the sprue).
For the Kombi-shootas I used 1/16" magnets on each side as pictured below. Its really important to get this aligned as closely as possible since 1/16" is so small. Otherwise they are pretty simple.
For the Big Mek I use a 1/8" magnet in the head and shoulders since i had the room to go bigger. A corresponding 1/8" magnet went into the Teloporta and Kustom Force Field, but the boss pole (for Meganob option) only has a 1/16" magnet.
Pics below, and I'm happy to answer questions in the comments below.