I had to add kde4-base eclass inherit to make qtcurve-qt4 work with kdeprefix (bug 260270). But this pulls in a dependency on qt-webkit, which is unkeyworded on alpha and known not to work on sparc. So I had to drop these arches for now, until that dependency is removed from the kde4-base eclass.
kde4-base.eclass no longer has a forced dependency on qt-webkit, so I re-added the keywords to the new version, 0.62.0