There are a few more parts on the air filter assembly for the civi GM trucks. Rubber bushing, noise resonating muffler, steel bracket that holds in place, hard plastic hose assembly, and the air collector on the core support on the passenger side of the radiator, that gathers fresh air from the front of the truck behind the front grill.
Very hard to find but the system is out there, used. I do not know if GM would stock parts new but maybe a possibility.
I removed mine from my 82 K30 and took 2 filter housings and used the inlet off the second and cut hole in the first and spot welded on making a dual snorkel air cleaner. Then connect flexible air ducting to the drain tile schedule 35 or 40 3 inch diameter 12 inches long to a y, then the original hard flex duct to the core support.
If you look at the original air cleaner of the 6.2 under throttle you will see that the top off the air cleaner flexes down because off suction. Inlet opening not large enough. Almost every 6.2 that I come across has stripped or scored air cleaner studs. I grab every good one I see in the salvage yards.
Does adding the second inlet help? Does fresh air to a diesel make a difference? I say yes, more air, denser air. I have not made the change to the CUCV, but may fab up the dual snorkel because the second inlet does have a positive effect.