Broadly speaking, you are correct. US Armour would have markings on both sides.
USAF aircraft of the time wouldn't have symetrical markings on the top & underneath of the wings.
Traditionally, Decalling is: paint model, apply gloss*, then decals, use Microscale Sol/Set as per instructions, cleanup, and gloss again, then mat or satin finish.
*Gloss where decals go or whole model.