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Are you talking about modern engines or engines back then?
If you are talking about modern engines, if it fits in but just won't line up with the motor mounts, you could always remove the old motor mount brackets, even if you have to burn them off with a torch and then move them to where you want and weld them back on. Just set the engine down, mark where the motor mount brackets must go, lift the engine back out and install them where they have to go.
They isn't some database to search for an interchange of something that far back and I don't even list that year fiat in any of my repair manuals, so unless you can find someone who has done it before, perhaps getting some ball park dimensions of the engine bay and seeing what engines you might want to have. Plus, you could always shorten of lengthen the driveshaft to fit at a driveshaft shop.