I have ferreted in La "Storia" and have the same photo labelled as a Fiat-Giannini entered by D.Ogna and C.Ogna in the 1954 Mille Miglia. That would suggest that it is a Fiat Special with Giannini modified engine rather than Giannini produced car..... although I have seen it on an entry list as just a Giannini.
However it seems the same car is probably from 1948 and has been entered in the Mille Miglia 4 times, in 1952 even under the same number. It has Fiat Topolino A chassis with a 750 engine, but its appearance has changed considerably from having cycle wings to its final barchetta version in 54 as shown in the photo.
I see it is for sale for 175K Euro !