Earlier Miranda lenses with the external PAD (like some Exakta lenses) can be used, but the release button has to be slowly pressed or a small stop-down button has to be pushed in if stop down metering is used.
The G does not have an internal meter. The meter-prism as on the GT and a non TTL prism can be used, which would also fit early letter series cameras.
The prisms and accessory viewfinders on the Automex and Sensorex are different and do not fit. The top of the Sensorex / Automex series was taller. Besides the pentaprism and metered prisms, there is a waist-level finder with a pop up magnifier and a critical finder with 5× and 15× magnification. Pentax M42, Nikon F, and Exakta lenses can be adapted and will focus to infinity. But they are manual lenses. A hearing aid cell can be used to replace the mercury cell.