This paper describes recent results in a project at KUBOTA to develop a multi-fuel gas engine driven Stirling heat pump. It is mainly driven by engine shaft power and is partially assisted by thermal power from the engine exhaust heat source. We have previously developed the D-3 machine, the fourth generation prototype of the heat-assisted Stirling heat pump. Performance simulations of the next (E-3) machine are presented in conjunction with driving engine characteristics. System matching and optimization criteria and constraints are discussed with implications for performance. This machine uses helium gas as a working gas and is constructed as two 3-cylinder sets, each a combination of two Stirling sub-systems (one a power producer and one a heat pump). Utilizing both shaft power and thermal power, performance is controlled by phase shifting of the hot-side pistons to adjust the absorbing of thermal power. This heat pump system is expected to produce cooling and heating water at high COP. Developing this machine will provide a CFC-free thermal utilization system technology that satisfies both wide heat demands and various fuel systems.