There's 2 versions of MorphOS one for A1's and PPC based computers and one of PowerUP Classic Amigas although the PowerUp version doesn't recognise a lot of the IDE adapters and has a strange registration system whereby it will work at normal speed for 2hrs and then after that it will slow down considerably unless you use the registration programme in MorphOS which means you have to be able to connect your Ami to 'tinternet.
For more info on PowerUP MorphOS goto http://powerup.morphos-team.net/. As far as i know as MorphOs was designed for Pegasos it should work with pegasosII