This is why I wasn't looking for a model name for this car. Its a good example of the difference in how a car was referred to at the time and how its referred to now, looking back. At the time, as you say, it would have just been called the Arzani-Volpini or Arzani-Volpini-Maserati but now it is sometimes (if not entirely inaccuratley) referred to as the Arzani-Volpini F1. To be honest I only included the F1 bit in the title so people looking on the forum would know its an F1/GP car.
Since racing cars aren't marketed to the public in the same way as road cars their exact type numbers are not as set in stone, especially in the 1950's. I remember reading a biography of one well known driver (Stirling Moss I think) who said that Coopers of the time were often not referred to by their type numbers but by their year and category instead(by the teams and drivers at least), ie a Cooper T51 would be called a 1959 Grand Prix Cooper. However today they are almost always referred to by their proper Cooper type numbers.
Plus don't forget Eccelstone may have invented F1 the brand but F1 the category has existed since the 1940's (it was originally but only briefly called Formula A). Grand Prix was the name of the championship and the races, Formula 1 was the name of the category and rules they were usually run to. They might not have always called them Formula one cars but they should have...