Ansaldo San Giorgio was a branch of Ansaldo of Genova, but had its premises in the Pistoia province. The shown trolleybus seems to have an Aerfer-designed body (nothing strange: both companies belonged to the State-owned group Iri) and Fiat 2401 or 2405 groups (we cannot say "chassis" because these models carried a self-supporting body). It is very similar to the small batch of Aerfer VE 811/Fiat 2405 delivered to Catania, Sicily, in the late Fifties.
Best regards,
Gliz