That is about 250*F, which I think would not trigger the internal regulator in a Nations/DC Power alternator, based on what we saw when we ran one, but it is pretty hot. DC Power says their alternators are not for battery changing, and infer it is because they don't want them at full output for long periods of time. DC power pushes them as for running big audio setups and such or at less than full output for offroad lights and things like that.
The Balmar trips at 220*F or so and goes to 1/2 power which is just enough to let the alternator cool enough, especially with the van sitting still. It is tough to cool down much when the alternator is attached to an engine at 200* in a 150* or more engine compartment. We have found on ours that if we run more than about 60% of rated output, we will get to 220* or a bit hotter. At idle it is tougher for sure as the engine compartment is hotter, as is the radiator that is blowing in hot air.
The cooling hose setups that I have seen put together, for the most part probably don't do much because they bring in air from the front of the van to the alternator. The alternator pulls air in the rear and blows it out at the pulley, so any cooler air would need to go up to the rear to the back of the alternator. Of course the radiator fan is fighting that, and moving air from front to back.
It may be that on the Chevy there is more room for a bigger alternator at the factory alternator location, as the lower mount is very tight, and some years are worse than others, like our 07 that has an extra heater shut of valve and a main wiring harness in the way. The OEM alternator could be moved to the secondary location as it is smaller.
All the more reason for the companies to go to higher voltage systems so the alternators are smaller and run cooler.