pl. (Mech.) Those pieces of a machine, or of any timber,
or stone work, which form corresponding sides, or which
are similar and in pair; as, the cheeks (jaws) of a vise;
the cheeks of a gun carriage, etc.

It looks like a drydock spec for a ship.
When a hole thru a steel plate (e.g. in a tank structure) is corroded (the diameter becomes uneven and bigger), the easiest way to repair it is to weld a doubler, i.e. a patch of steel with a new made hole of the original size and shape.
In this case, it looks, they require one doubler at each side, so they name it "cheeks" (see definition for cheek above)
Parches de chapa (de acero) 5 1/2" de diám. x 3/4" de espesor con orificio de 2 1/4"
Hope it helps!