Heat exchangers are essential to transfer thermal energy between working fluids in applications ranging from aviation to power generation and storage. Recent demand for more efficient yet extreme thermodynamic cycles has necessitated the development of compact, ultrahigh power density heat exchangers capable of operating in high temperature, high pressure conditions. While recent work has demonstrated the feasibility of such heat exchanger cores in a variety of materials using coextruded, etched, or additive methods, integration of heat exchangers into system cycles via manifolding remains an ongoing topic of discussion. Specifically, the need exists to develop manifolds that connect to standard tubing using existing cycle connection techniques while uniformly distributing working fluids and minimally contributing to pressure losses in the heat exchanger assembly. In this work we present the design and evaluation of one such manifold subassembly, for use with a multiscale ceramic heat exchanger core in a sCO₂ Brayton cycle. By using finite element numerical simulations to identify and iterate key geometric parameters, an optimized manifold is predicted to achieve significant flow distribution (S* ≤ 5%) while maintaining negligible pressure losses (ΔP_loss < 1%). Furthermore, this manifold design relies on proven manufacturing methods and low cost materials, enabling a high degree of customization based on application without inhibiting performance of the heat exchanger core.