Back to the original post. But first, a bit of history. (FF members are now logging off in their droves and going to bed.
Having had the original Viva, complete with 1256 cc of pulsating power all 58.5bhp of it......trust me, in that car the .5bhp was important, a Chevette, again still with the same engine and a Chevette HS2300 with a significantly breathed on engine I've had more than a few Vauxhalls.
I was always a fan of the slant-4 engines and, in my opinion, they were sadly underdeveloped by the factory. Blydenstein Engineering (the de facto factory competitions arm of Vauxhall) enlarged the 2300 out to 2.6 litres and produced some (for the time) considerable power and torque improvements.
However, it was in 1979 when I went to work for an Opel dealer in Manchester that I got the new Opel Kadett as a company car. This was a revelation in as much as it was FWD and its engine was a real fizzer that just begged to be revved and in some respects was redolent of the Alfasud engine.
At 1.3 litres it put out 75 bhp and, although that might elicit shouts of "Big deal" you have to put that in context by remembering the Chevettes 58.5bhp and similar outputs from Ford, Chrysler and BL. To get 75 horses in the Vauxhall/Opel range you had to go to the Cavalier/Ascona 1600 and to get that power in an Escort you had to go to the Mexico.
That motor was what became known as the "Family 1" engine, later 1600 1800 and 2000 versions were Family 2". After a while the 1.6 came from the "Family 1" block as well. But what also crept in almost unannounced was a 1.6 diesel which outwardly was very similar to the petrol engine; it was a belt driven SOHC motor.
That engine is, I believe, what the current 1.7 derv drinker is derived from. At the time when FIAT and GM were having talks, they had the 1.6/1.7, a 2 litre and a 2.2 diesel, and from memory they weren't held in particularly high regard. Someone I still work with had a Vectra with the 2 litre and it would struggle to better 42mpg and was a pretty coarse unit. FIAT had a pretty up to date diesel range but some of their petrol engines were looking a bit dated.
There was the FIRE, obviously, but the rest were probably getting a bit long in the tooth, the Alfa V6 was introduced in 1979, the V6 that appeared in the Lancia Thema was the Peugeot-Renault-Volvo unit that (I'm willing to be corrected here) powered the Peugeot 604, Renault 30 and Volvo 960 as well as......possibly......the DeLorean. The 2-litre four cylinders were descended from the Aurelio Lampredi designed engines which themselves started life in 1966.
So Vauxhall had some badly thought of and old diesels and FIAT had the same problems with some petrol motors, and I think it's safe to say they were thinking about development costs so maybe they became a perfect fit. From a political point of view, I don't think there was any way that Ford would collaborate with their mortal enemy and perhaps the same was true of VW.
The last Alfa V6 was actually a Holden derived engine with some considerable modifications carried out in Milan and the 2.2 inline-4 used in the 159 and 166 was from GM (Europe).
The 1.3 MJ seems to have been made exclusively in Poland and by FIAT in India, as I believe is the 1.6 MJ, whereas the 1.9 MJ was made in both Italy and Germany. The 2 litre GM and FIAT versions were developed separately after the two companies broke ranks.
Just out of interest, well it interested me anyway, Common Rail injection as a mechanical principle dates from around the time of the First World War as Vickers used the idea in their submarines around 1916 and some trucks used it in the late '80s - early '90s, but it was probably FIAT that first brought out the electronically controlled system that we know now, before selling it to Bosch who developed it.
So the answer to your question is perhaps not that simple, beacause as is the way with these things, the two partners will have made modifications to the own version of an engine, but, I'd say that all of them are, or were in their original forms FIAT diesels, with the exception of the 1.7 which dates back to the Isuzu 1.5 and 1.6 engines in the Cavalier, Astra and Corsa.
This started out as a brief note as to which engines came from Italy and instead it turned into a ramble.