I have a few more info
F.C.B. is of course Fratelli Comerio Busto Arsizio.
I have found an advertising page in a rare magazine called Motor Scooter e piccole cilindrate dated July 1950.
Microvettura da corsa F.C.B. cmc 125
Engine Innocenti,
Gearbox 3 speed
Track 104 cm.
Wheelbase 174 cm.
Tyres 3.50 X 10
Chassis Tubular
Weight Kg. 125
Tank capacity 10 Litres
Speed Km. 70/80
There is at least another one nearly complete in Northern Italy.. I know for sure because I helped a friend buying one in the 1980'.