Found some comparison spec run downs on the engines this might help.
Now a 351 Windsor is really a slightly enlarged 289/302, as it's name implies it comes from Fords "Windsor" engine family (a.k.a. the 90-degree V engine family). The thin-wall cast SMALL BLOCK accepts regular sized spark plugs, uses a timing chain in the block, routes water through the intake manifold, features thin main-bearing caps, a very good oiling system, and uses the same heads for 2V & 4V versions. The heads are are small, utilizing in-line valves with relatively small ports. The valves are 1.78" intake and 1.54" exhaust, i.e. the same size as a 289/302. The valve covers are straight (front to rear), attached by 5 bolts, and when removed you can see 351 cast in the lifter valley. The small side-by side (in-line) valves are the dead give-away.
Engine History & more specs
- 5-bolt straight valve covers
- radiator hose to the intake manifold
- regular 5/8" spark plugs
The 351 Cleveland, on the other hand, belongs to Ford's 335 engine family. This thin-wall cast BIG SMALL BLOCK uses the smaller 14mm spark plugs, has a separate front cover (bolted to the block) housing the timing chain and routing water - so that water does not go through the intake manifold, features beefy main caps (wide enough to drill for 4-bolt mains), a poor oiling system, and uses different heads for 2V & 4V versions. The heads make all the difference and these fire breathing babies make this motor the legend it is. On the 4V, the valves are HUGE, measuring 2.19" intake and 1.7n" exhaust (don't remember exactly). Valves this large are only possible via a canted valve arrangement, forming what Ford refers to as a "poly-angle" combustion chamber. The valve covers are not straight - the front is flat and parallel to the ground, but a curve twists the rear parallel to the head. They are attached by 8-bolts and when removed, there is a 4 cast into the corner of the 4V and a 2 cast into the corner of the 2V (at least in 1970). The canted valves are the dead giveaway.
351 Cleveland Specs and more info
- 8 bolt 2-plane valve covers
- radiator hose does not connect to intake
- small 14mm spark plugs