I have sent you my infos to your puzzle previously:
Frua drew a 2-door hatchback-version (X2L) for Glas, based on a Glas 1004, in 1965. Two years later (Glas has been sold to BMW), Hans Werner Bönsch remembered about these drawings, and developed (together with Wilfried Ball) a hatchback-two-door-limousine, based on the X2L-drawings of Frua.
The base was still the Glas 1004 (you see the 5 wheel nuts, instead of 4 on the BMWs). At first, they planned to use the 60-HP-Glas-engine of the Glas1304, later they chose BMW M10, out of the 1600-2.
Conclusio: Glas (base 1004)/BMW (engine) with Frua-based-bodywork, restyled by Bönsch and Ball
BMW 1600 Studio 1971