An important arithmetic component of “Arithmetic and Logic Unit” or ALU is reconfigured in this paper, known as “Full-Adder-Subtractor”, where an advance low-power, high-speed nano technology “QCA” with electro-spin criterion is used with reversibility and the advancement of multilayer 3D circuitry. In this modern digital world, this selected nano-sized technology is an effective alternative of widely used “CMOS Technology” because all the limitations, mainly limitation due to the presence of high power dissipation at the time of device-density increment in a “CMOS” based integrated circuit, can be optimized by “QCA” nano technology with electro-spin criterion and this technology also supports reversible logic in multilayer 3D platform with less complexity. This paper, primarily presents two novel “QCA” based 3-layered “Adder-Subtractor” designs using the collaboration of multilayer inverter gates, reversible modified 3-input Feynman-Gate and 3-input MG (Majority Gate) with very less cell-complexity, area-occupation, delay and energy-dissipation and high output-strength, temperature-tolerance and accuracy. A clear parametric investigation on presented designs are shown clearly in this paper through a comparative manner with some previous published related structures. Additionally, another parametric-experiment on a novel multibit reversible multilayer “QCA” based “Full-Adder-Subtractor” circuitry using the working phenomenon of “Ripple Carry Adder” (RCA) and multibit subtractor (“ripple borrow subtractor” or RBS) is presented in this proposed work in a proper way and this combination of RCA and multibit subtraction operation converts the proposed circuitry into a hybrid form, which is more effective compare to some other advanced adders in parametric-optimization field.