WOW WOW WOW!
Italian Hb refrigerated vans in OO! Really beautiful! It was the refrigerated version of the Fb van, the "British Loading Gauge" version of the ubiquitous F type van.
Here there is a preserved Fb, still unmarked - they are waiting for the registration of the rolling stock before paint markings, since it will run as bicycle transport on touristic trains - https://www.societavenetaferrovie.it/carro-21-83-21-48-963-3-fb-1931-sagoma-inglese/
Warning, the top model is for a continental F van, the lower one for an Hb.
In real life, Fb vans are a bit narrower and lower than the F counterparts. As for lenght I have still to check since the only restored vans in SVF fleet in Primolano are an Fb and and FF (longer, for parcel services). There are indeed F pattern vans in Primolano, but they need restoring and are seldom coupled with the restored ones, so rough lenght comparison was impossible.
Roco and "new Rivarossi" use 1:87 and I am unsure if Roco makes an Italian F van. "Old Rivarossi" used 1:80 scale. Hornby acquired the "new Rivarossi" molds. H0 dimensions should be multiplied by 1.145 theoretically, but since the Fb should be roughly 2 inches narrower, this means that a correctly scaled H0 Fb should be 0.64mm narrower than an F.
Those who consider altering a preexisting H0 F van might consider working on the kits shown in this page (it is advised to use supplied plastic wheels since metal ones might wear out the "bushing"): https://www.duegieditricestore.it/50-kit-ttm/