There's no doubt that America is home of the big-ass V8s. In 1932 Henry Ford started making V8 engines so cheap that almost everybody in the United States could afford one. But for some a standard V8 wasn't enough. Starting at the end of the 1950's and running through most of the 1970's you could opt for a "big block" V8, which was bigger than your average V8 in both displacement and physical dimension. The whole concept of a big block V8 in post-war Europe must have seemed alien. Despite this two example existed.
Rolls Royce/Bentley Six and Three Quarter Litre (1959-present)
Around the same time that American big blocks started popping up, Rolls Royce introduced a V8 fit a luxury marque such as themselves. Initially the engine displaced 6.25 litres, and was increased to 6.75 in 1968. Arguably this engine is the longest running production engine ever (Chevrolet's LS engines being far removed from the original small block). It's also the second largest V8 and only big block in production today (Chevy's 7.0 LS7 being based on a "small block).
Mercedes 6.3 & 6.9 (1963-81)
In the 1960's if you wanted a big non-American luxury car you had two options; Rolls Royce/Bentley and Mercedes. And just like Rolls Royce, Mercedes offered a big engine to go with their big cars. The engine started out life powering Mercedes's biggest limosines, but it's peak came while powering the outrageous "Red Pig" touring car.
If you can think of any other big post-war non-American V8s let me know.