I wouldn't call that a 'blatant rip-off'. It was a fashionable design in 1967. There some styling elements it has in common with the Mangusta,
(similar intakes behind the side windows, a horizontal beltline dividing the body in a lighter part above and darker part below )
but the over all proportions are different like the front treatment and most of the other parts of the car.
Second page shows another attempt of the G.31 project penned by Pio Manzu.
The first was almost completely done by Werner Hölbl who worked at OSI at that time.. The car was based on a Fiat 125 mid-engine platform. G.31 started as an exclusive FIAT project originally initiated by Dir. Ing. Dante Giacosa under collaboration of Ing. Sartorelli and Sergio Cattaneo. Alas a still-born project it was later transferred to Autobianchi, but never made it to production.