The K&Ns flow well because the filter media is cotton gauze. Put it under a magnifying glass and you'll see large gaps between the unevenly "knit" gauze. These gaps let more dirt pass than reasonably clean paper or foam filter elements. The gaps also move more air which usually improves performance at the expense of cleanliness.
As you must well know, Toyota engines have great longevity. FWIW, I'd replace that K&N filter with a quality paper filter immediately since the K&N filter is just letting more dirt into the cylinders than quality paper/foam elements would allow. If left alone, that extra, and perhaps larger consistency, daily dirt will abnormally increase wear and tear over time. NAPA/Wix make good paper filters. So does Toyota oem replacement. Other good brands exist. Avoid Fram/Pennsoil and other cheapies. Quality foam filters are a viable option. A search on "K&N filter" in Gen 4x4 should bring up threads that hashed all this already.
If you don't go snorkel, you can extend the '78 AC housing horn to the gap between the bib and the hood to catch cool air. IIRC, some late '70s and the '80s FJ40s came with extentions that connected the AC housing horn to the bib with a horizontal slit opening to catch the air coming inbetween the bib & hood. I've been wanting to pick up such an extention one day for my '77 40.