Just went out to my '97 K2500 7.4L. I suppose it may be different from small-block air filter housings.
I have the "Second Design" (smaller) Delphi air filter housing as shown in the link in Post 12 by df42x4.
My SPID tag shows "K47".
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And the filter housing is molded with both air filter part numbers.
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I bought the truck
very used, so I won't promise that the air filter housing is original...but I have zero indication that it isn't.
I conclude that ordering "K47" on my vehicle gets you a bigger air filter, not a different air filter housing. But what do I know?
[Much-later edit] I tried crossing the number on the existing air filter to something recognizable, but had no luck. According to the Tape Measure, it's the equivalent to the A1300C, the smaller of the two possible filters.
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This air filter was what was in the truck when I bought it. I knocked the loose dirt and insects from it, and it'll go right back in.
[/Much-later edit]