Parabolics often give a mild lift. Further to this the military 109 chassis have extended spring hangers and shackles (as do One Ton examples). For a big lift, you could consider putting the springs over the axle rather than them remaining underneath.
The problem with any lift however, is that it affects your centre of gravity. I would suggest you seriously consider whether or not it is worth the extra time and expense to go beyond the parabolic "lift".
As for disc brakes. I don't know much about these conversion kits. From what little I've gathered from people I know who have looked into it, it is very very expensive. It's something I've never felt would be a problem - but I tend not to have my 88 axle deep in mud or silt.