This paper demonstrates the application of an integrated rotorcraft multidisciplinary design and optimization framework, deployed for the purpose of preliminary design and assessment of optimum regenerative powerplant configurations for rotorcraft. The proposed approach comprises a wide range of individual modeling theories applicable to rotorcraft flight dynamics, gas turbine engine performance, and weight estimation as well as a novel physics-based stirred reactor model, for the rapid estimation of various gas turbine gaseous emissions. A single-objective particle swarm optimizer (sPSO) is coupled with the aforementioned rotorcraft multidisciplinary design framework. The overall methodology is deployed for the design space exploration and optimization of a reference multipurpose twin engine light (TEL) civil rotorcraft, modeled after the Bo105 helicopter, employing two Rolls Royce Allison 250-C20B turboshaft engines. Through the implementation of single-objective optimization, notionally based optimum regenerative engine design configurations are acquired in terms of engine weight, mission fuel burn, and mission gaseous emissions inventory, at constant technology level. The acquired optimum engine configurations are subsequently deployed for the design of conceptual regenerative rotorcraft configurations, targeting improved mission fuel economy, enhanced payload-range capability as well as improvements in the rotorcraft overall environmental footprint, while maintaining the required airworthiness requirements. The proposed approach essentially constitutes an enabler in terms of focusing the multidisciplinary design of conceptual rotorcraft powerplants to realistic, three-dimensional operations and toward the realization of their associated engine design trade-offs at mission level.