It is a first series 1900 SS, with 1975cc motor...actually making it a 3rd series Touring bodied 1900 coupe.
The 1st series is a 1900 CS, with 1884cc motor and doors that extend through the running board. Some other body and mechanical details are different.
The 2nd series is also 1884cc, and is identical to the 1st series, except the doors stop at the top of the running boards.
The 4th series looks something like a big Giulietta spider and has the 1975cc motor. Mechanically, the 4th series cars are identical to the car pictured.
The motors in all of the 1900s are similar to the later 102 series, but they have the old style valve trains, like a 6c2500 and earlier Alfas. Series 1 are the rarest, but prices are similar for all four series cars.
What is the owner asking as to price? The car looks superb!