Port Companies were essentially stevedoring units. Their principle duties were loading and unloading material and equipment. Port Companies were organic to the Transportation Corps (TC). "Longshoreman" was his Military Occupational Specialty (MOS) and "271" was the administrative identifying number for that particular MOS at that time.
Upon return from overseas, individuals not eligible for immediate release from active duty were randomly assigned to local units and their MOS's were often changed accordingly. This was usually purely procedural and individuals performed few, if any, duties in these temporary assignments. Your Dad was assigned to the 206th because (1) it was a local unit and (2) being a patient, he couldn't properly be assigned to Welch. The 206th served simply as official custodian of his individual service record during his stay at Welch.
Okinawa Shima is one of the Ryukyu Islands. "Ryukyus Campaign" is the official designation for the assault and occupation of Okinawa Shima, Ie Shima and other objectives in the Ryukyus between 1 April (Easter Sunday) through 2 July 1945 (the Air Offensive extended from 26 March through 2 July 1945).
Your Dad would be entitled to the Purple Heart, Asiatic-Pacific Theater Medal with one bronze service star (Ryukyus Campaign) and the World War II Victory Medal. Eligibility for any decorations and awards not listed on his separation papers would have to be determined from official records.