According to Abarth: the Man and the Machines, (p164) the car was produced to provide a sporting coupe that was of better build quality and drove more quietly than the 750 Zagato, which was an alloy bodied car. It was designed by Michelotti, built by Allemano on the Fiat 600 chassis, and was introduced at the Turin Auto Show in 1959. Weight was 600kg and top speed was 160kph, with a 4.56:1 axle ratio. Engine was a Fiat 600-based unit enlarged to 847cc and produced 57hp at 6500 rpm.
What kind of engine is in it now? I am a little confused regarding whether the Fiat 600 engine was ever enlarged to 850 or whether it was only the 600D engine that was. I thought it was the 600D, so I'm not sure how Abar'th would have made an 850 engine in 1959, since the 600D didn't come out until late summer 1960.
This is quite a rare car, I believe. You should buy it if it appeals to you and the price is realistic.
Jim