I still haven't been able to find more information on the origins of this car on-line but I came across the website of the coachbuilder Aprile. They state that the bodywork dates from 1953 but I think this may be a typo for 1935.
I would imagine that the original car was a fairly unexciting saloon or tourer and can't imagine that a Zagato bodied 6C 1750 would have been rebodied in this way unless it had been badly damaged.
I'm still searching..........