From memory (and I'm not sure I can trust that now) the figure of 1,200 comes to mind. That worked out at 1,000 for Japan, 50 for UK and the remaining 150 for Italy and rest of Europe.
I was in the process of tracing every Saturno built and had quite a list of exact model, chassis/engine numbers and owner/location but had a severe computer crash and lost everything from the hard drive. Not to worry thought I as I had backed up all my folders on an external hard drive, only to find out that all that was backed up were the folders, but all were empty.
I can say that each Saturno was handbuilt by a team of 6 who worked on a metal (sometime wooden) table, even had pictures of that process but alas, all again were lost. Paul