Let g be a complex simple Lie algebra of classical type, U(g) its enve
loping algebra. We classify the completely prime maximal spectrum of U
(g). We also construct some interesting algebra extensions of primitiv
e quotients of U(g) and compute their Goldie ranks, lengths as bimodul
es, and characteristic cycles. Finally, we study the relevance of thes
e algebras to D. Vogan's program of ''quantizing'' covers of nilpotent
orbits O in g.