GM thought the extra cooling passages were necessary, as was a higher-cooling fan-blade, and a higher flowing water pump, and larger diameter hoses, ". . . to increase cooling capacity for the higher heat rejection of this more powerful engine . . ."
Yes, we might get by with lower capacity replacement 235/216 water pumps and hoses and fan-blades, and no extra cooling passages between the larger siamesed cylinders, but GM upgraded these things for a reason (and, back then the reason was not to sell more/different parts). These engines were meant to be used in the largest trucks, under the highest of loads, often at high rpms at low speeds.
On the other hand, it is hard to understand why different baffle designs were used in pans for various 235/261 engines, especially since the oil capacities do not appear to be significantly different. And, it does not look like the oil pumps and pick-ups are different.
