Seeking father's OSS & military records

My Dad was an OSS Intelligence Officer, (9302) which morphed into counterintelligence after the war ended.  I have very little information regarding his assignments or duties for obvious reasons.  He did keep a diary and made limited notations and entries.  He joined the 15th Army Group HQ on December 27 sharing an apartment in Siena, Italy.  From his diaries, he was in Siena and on January 30 1945, a roommate, Bob Amerine moved in, then in early February moved to Florence.  He makes a note that on February 2, there was a party for Colonel Smith.  On February 12, General Marshall visited, there was a parade of sorts....  On March 3, 1945, he mentions interrogating a PW but no other information.   He had dinner on a few occasions at Grecco's which I could not locate... thinking it was a now defunct restaurant.

Here is an excerpt from an extended interview conducted with my Dad in 1990:

FJL Interview::: We were stationed in Florence then we moved the HQ at end of war to Salzburg then into Vienna as occupation forces in Austria - at the minute war ended, Intelligence ceased to exist, became Counterintelligence.  My responsibility along with another agent at OSS John Hine, the two of us were responsible for the denazification of Austria… HQ at US occupation forces of Austria… set out to give commands to the OSS troops around Austria that were established had to  designate based on Potsdam agreement, who should be arrested, this was done on an organizational chart, very complicated, if we had computers in those days it would be simple, I  devised card OSS units when arrested someone, would interrogate, found out who was predecessor was, particular job, who followed, who was the boss, and who was under him so to get complete Nazi organization from time of Anschluss in 1938 to present time.  In Vienna, same set up as Berlin, four power English, French American Russian… made life difficult… Russians were terrible  stole trains as they came into town…. Russians surrounded territory …  left came back Feb  46

He received his promotion to 1st Lt at a ceremony from General Mark Clark on 1945-04-20. Where can I find additional information on locations and duties?  Thanks so much.