Milhouse, the link you have posted is for a splined cassette, which is
not suitable for a Magic Pie. GM recommend a 6 speed thread-on gear cluster known as a "freewheel" which simply screws on to the Magic Pie's threaded boss.
![](http://www.sheldonbrown.com/images/freewheel-vs-k7.jpg)
The special tool is only needed to remove the freewheel
(when it fails and needs to be replaced).
I couldn't find anything suitable on bikeshop.no, but I found this
Shimano MFTZ06 6 speed screw-on freewheel on woollyhatshop.com which should fit the Magic Pie.
The
7 speed freewheel can be fitted if you use an extra spacer washer on the axle, but the 34 tooth 1st gear can be a bit too large for some dérailleurs to cope with.
![Wink ;)](https://goldenmotor.com/SMF/Smileys/default/wink.gif)
The following picture shows a 7 speed freewheel unit being screwed onto the hub:
![](http://www.arhservices.co.uk/GoldenMotor/13-34.JPG)
Hope this helps.
Alan