Correct and when it came to XB's.
4V didn't mean big valve, big port heads. It just meant 4 venturi (4brl carb/manifold). It's the most common mistake.
4V heads were very rare in XB's due to changes in emission laws. In 1975 the canister was implemented and the 351 OC 2V head was born (made a definate).
Some luxo barge 351's had the 2brl as those weren't made with performance in mind.
Brenden