To operate the upgrade movement, you need a different stem in the crown. I have made crowns that have an S engraved, and with the same stem, the 7S26 movement can also be operated (so this crown can also be used to make your standard SKX nicer).
In the crown, a stem is installed. This works OK with movement from watches that have been used for a while, but with new movement, I noticed that it gives not enough pressure to lift the crown release lever. So a longer stem is needed to build up more force (I add a stem when bought alone, this can be cut to size, 14,5mm instead of the 14mm that it is when it is delivered).
This crown is the crown that needs to be ordered in combination with the movement upgrade.
Available colours for the S are Red, Blue and Black. Also no colour, that you can fill with a colour (or not).