A die group with a forming head for forming a tubular parison made of plastic material with a female die, which defines an internal through-cavity with a vertical die axis, a female die holder element, rigidly connected to the female die, and a housing body which defines a vertical reference axis for coupling with a distribution duct of the forming head and supports the female die holder element allowing relative movement thereof in a longitudinal/transverse plane. A first electric driving actuator is supported on the housing body and rotationally drives a first output element coupled with the female die holder element by means of a first transmission mechanism so as to move the female die holder element in the longitudinal/transverse plane with respect to the housing body, in accordance with a first isometric transformation.