The OBS (80's) had more airflow than the 90's and could get away with less cooling. When you step out of the freezer electric fans are not recommended for IDI's as they simply can't flow enough air with the space and alternator constraints. Going to a 9 blade 21" fan is nearly a required mod. It's possible the new Ram diesel electric fans may do ok, but, they already are running hot towing. The electric fan choice has GM $hitty cooling design written all over it.
On a scientific note electric fans peak at 5000 CFM without restrictions like radiators. I measured a 21" Trailblazer fan at 10,000 CFM with the hood closed. I used the fan on my 1993 and it didn't have enough CFM to keep it cool - not enough blade pitch. So the 6.5 TD requires way more than 10,000 CFM to stay cool. (Then we turn on the AC!) Conclusion is 2 electric fans will not keep you cool when you need max cooling. So going electric is reducing cooling performance. You may not need all the cooling performance depending on your use and outside temps.
Other things reduce cooling load like a better turbo and better exhaust to let heat out of the engine.
Some plow truck operators have had to mod their fan clutches due to the airflow changes the plow caused on the freeway while going to the next job.
