Big block cooling issues

Still doesn't work that way. The only reason to restrict the velocity of the coolant is to avoid cavitation and turbulence issues. Not heat transfer per se. That is driven by the temperature differential between the hot side and the cold side. The radiator has to be large enough to transfer all the heat between a 180F coolant temp and (say) 100F ambient temp. The cylinder heads run a lot hotter than 180F so they don't need as much surface area.

In fact, if coolant moves TOO slowly then there can be hot spots and localized boiling in the heads - which also reduces the amount of heat carried away!

The only engines I have ever seen that don't run dead cold with the thermostat removed have a secondary disk attached to the moving t-stat element. Old Mercedes diesels, IIRC. This disk opens a bypass when the stat is closed - so the bypass is shut off when the stat is open. With the stat completely removed the large bypass stays open all the time and a big percentage of the coolant flow is diverted away from the radiator.