I probably have some "film" pictures of the prototype engine from my visit to the factory. It was/is sitting on a stand next to a bunch of other hardware that they came up with. (that also never made it to production. Flat opposed 8, overhead cam Cleveland setup....)
It is an aluminum V8 block and heads, spec'd very similar if not the same as a Ford 302. I do not believe that any every hit a car, even the early production. They got the HIPO 289 as it was an "off the shelf" piece that was later replaced by production 302-4V Mustang/Cougar stick motors with and without smog (air injection) stuff.
I also have a homologation doc that shows some old nasty webers and other parts that were evidently proposed for use, or perhaps as optional equipment. It's all in Italian so I haven't been able to translate too much.... Good pic's though!