Actually, not to speak for Bond-o, but the bigger issue is simply that the 120 is not found in cars. The 120 and the 140 are interchangeable, but the 140 (3 liter) isn't used in cars either. As mentioned above, it is found in industrial applications (fork lifts, etc).
The problem isn't as simple as "a car engine will not work" - because many engines are in fact used in both cars / trucks and boats. The 350 is a prime example. Nothing special that makes it a "marine" engine except the cam, core plugs and head gasket. (And the externals of course - but I am talking about the long block).
Back to the original poster's question - don't get confused with the engine many call the "Iron Duke" - it is not the same.
