The 3 GJ target with low repetition rate and thick liquid wall chamber presents the mainline choice for the Z-Pinch power plant. An engineering scoping assessment has been developed for two candidate breeders (Flibe (F4Li2Be)molten salt and Li17Pb83 liquid metal) to identify the design requirements and optimize the components' dimensions. Several important engineering features have been incorporated to improve the Z-Pinch performance. For instance, an advanced high-temperature steel-based structure could operate near 800°C, an advanced power cycle could achieve high thermal conversion efficiency approaching 50%, a low-activation F82H-based steel with controlled impurities will generate only low-level waste, and an innovative idea has been developed to establish jet flow using a sluice valve. This paper identifies self-consistent reference parameters and documents an interesting comparison between the candidate breeders, highlighting the fundamental differences in performance and the benefits and drawbacks of each breeder.