I've been looking into my source but it maintains this is a Zagato-bodied Fiat 8V spider, although it may be 1953 rather than 1954. So it seems Zagato used pretty much the same body style for both a Maserati Spider and a Fiat 8V - unless someone can prove otherwise!
Here's another picture of the same car; there are one or two details differences but maybe it just wasn't quite finished yet..