Yes, Wanda, it looks like you are on target with this new information.
Again with Stanton as reference:
355th Engineer General Service Regiment: departed NY P/E, 21 Oct 43; arrived England, 3 Nov 43; landed in France,5 Jul 45; Belgium, 1 Nov 44; Holland, 5 Mar 45; Germany, 10 Mar 45, where inactivated, 17 Jun 46. Location at war's end, 15 Aug 45: Monchengladback, Germany.
NOTE: Unit was programed to deploy to South Pacific under Shipment #R8485-E, for the projected (OCT-45) invasion of Japan.
Normandy, Northern France, Rhineland, Ardennes-Alsace and Central Europe.
358th EGSR: departed US, 1 Jul 43; arrived Scotland, 6 Jul 43; arrived England, 8 Jul 43; landed France, 24 Aug 44; Belgium, 27 Nov 44; remained there for the duration; arrived NY P/E, 1 Jan 46; inactivated there 2 Jan 46. Location 15 Aug 45: Antwerp, Belgium.
NOTE Unit was also scheduled for shipment to South Pacific, per shipment #R9850-G.
Campaigns: Normandy, Northern France, Rhineland, Central Europe.
He was not credited with Ardennes-Alsace (16 Dec 44 / 24 Jan 45), so we must assume that he was NOT with the 355th for that campaign.
Try matching departure/arrival dates on his discharge, and you should come up with which unit he travelled.
You may also want to try matching the family letters by date to his tenure.