Maybe there's an explanation for two types of 351ci V8 engines in 1970-80.
If you're into all kinds of 1960s and '70s muscle cars, surely you've noticed the similarity between an Oldsmobile Rocket V8 and Ford's 351 Cleveland. Both have a timing set surrounded by iron and a fuel pump mounting location with 12 and 6 o'clock bolt hole positioning with one threaded stud. Also note the Cleveland's canted poly-angle valves and wedge chambers just like a big-block Chevrolet V8.
How do we explain these features common to both Olds and Ford V8s?
Semon E. "Bunkie" Knudson - whom Henry Ford II hired away from GM to run Ford in the late 1960s - brought GM engineering and styling talent with him. Knudson's own Larry Shinoda brought us the Boss Mustangs of 1969-71. However, we're convinced a whole lot more came from GM at the time. Study Ford's of the 1970s and you will see GM influences in both engineering and styling.
Why on earth would Ford develop a sister engine to the raised deck 351ci Windsor introduced in 1969 - the 351ci Cleveland of 1970? When you study the 351C's (and also 351M and 400M) architecture, it is virtually identical to the Oldsmobile Rocket 330/350/400/455ci V8 engines in front. The timing package is wrapped in iron, just like Oldsmobile. Cylinder heads are virtual knockoffs of the big-block Chevrolet 396/402/427/454 with poly-angle valves and tight wedge chambers.
Although it has never been proven and we've never found anyone at Ford who knows anything about it, we're convinced there was some kind of political struggle at Ford over the 351W versus 351C engines in the late 1960s. Ultimately, HFII would fire Knudsen in 1970 and enlist Lee Iacocca from within to run Ford. When Knudsen left Ford in 1970 and Lee Iacocca took over as President, the Cleveland and M-Series engines were gradually phased out leaving only the 351W in the end.