Maybe someone put a 20R head on the 22R block and kept the valve cover from the head... And just to inform, the 22R originally came with the dual row timing chain in 81-82. You can easily adapt pre 85 22R to a dual row chain by simply swapping out the oil pump drive spline to the narrower ones from any 20R and 81-82 22R's.
Jeff

It's all good!
83 Shortbed stepside lots of mods
82 Shortbed fully restored
85 Shortbed daily driver
88 4-runner-Wife's daily driver