Well in that case, there were no Soldier specific leg, thigh, or Forearms in Halo 4.
Even Halopedia's description of the Halo 4 and 5 Soldier set just list those components as a "Unknown" and only lost the Helmet, Chest, and Shoulders as specifically ad the "Solider" variant, which is why the The Armory entry for the Halo 4 Soldier only has those 3 parts.
SOLDIER-class Mjolnir is a variant of the MJOLNIR Powered Assault Armor that was developed by the Materials Group.
www.halopedia.org