Jeez. That's a 43 US gallon tank. My pick up only has a 36 USG tank on it.
Everything back then had rev limiters on them for just as stated, insurance companies. The big Chevies, Olds, Buicks, Fords and Mopars had at least another 25%-30% more power in them than advertised. Remember reading in the spec books, 400 advertised BHP? It was really closer to 460. And that was HP at the crank. It's what hits the ground that counts.
Oh, and the Cleveland engine had different heads on it too. The plugs were slanted in at an angle whereas the Windsor used a straight on plug.