Mika,
The oil filter assembly was utilised by Abarth to provide a better oil filtering solution. In addition it had a thermostatic valve that only allowed oil to travel to the oil cooler after it had reached a certain temperature.
The Flavia assembly is usually mounted on an aluminum or magnesium mounting block. Oil enters it directly from the pump and first goes through the over pressure relief valve. If the oil pressure exceeds approx. 80 PSI, then oil the pressure is relieved and the oil is returned to the sump. Next the oil goes through the filter. Once through if the oil is cold it will go directly the the main bearing oil gallery. Once the oil is hot the oil will first go to the oil cooler before returning to the main oil gallery.
Note: The oil filter elements are still available from several sources. The same element is used on some farm tractors as well. The o-ring in the lid is getting hard to find, so do not damage it if possible. Later model Lancia Flavias had the same valve assembly, but used a modern spin on filter instead. I use one of these assemblies on my engine dynamometer. You can see some photos of the dynamometer on my site at
www.scuderiatopolino.comHope this helps.