Hi Pat, one number is all i need. Here is the chronological locations of APO 887:
APO 887
London, England, 15 April 1942 - 1 Sept 1944
Valognes, France, 1 Sept 1944 - 16 Sept 1944
Paris, France, 16 Sept 1944 - 27 March 1947
Liege, Belgium, 27 March 1947 - 28 March 1947
ceased operation 28 March 1947
The letter he recieved from your grandmother was sent to Paris.
Valognes is a commune in the Manche department in Normandy in north-western France.
It lies on the Merderet river, 20 km (12 mi) southeast of Cherbourg.
After D-Day the platoon was most likey first under command of "ADSEC" (Advance Section, Communications Zone) until tranfrred to the permanent Base Section in Paris. http://en.wikipedia.org/wiki/ADSEC
If he was stationed in or near Paris, the platoon was most likely under command of the Seine Section which arrived in Paris 25 August 1944.
http://www.lonesentry.com/unithistory/seine/
There are some records availible for these Base sections but it will take awhile to locate & go through them.
Larry