Hi.
First, the 291st, if I remember correctly, was a 'Corps Engineer outfit. Keep in mind that there were echelons (levels)in the Military. Each Army was made up of Corps AND support units like quartermaster, engineer, anti-aircraft, Ordnance and artillery units. Each Corps controlled infantry and armored divisions AND support units just as in the Army. Each division included a similar mix of support units as well as three infantry regiments.....
An Engineer BN was attached to and considered part of each infantry division; Engineer (combat) groups were part of the Corps support units. So each echelon had engineer BN's. The 291st was part of the 1111th Engineer Combat Group, attached to VI Corps. The 1111th Engineer © GROUP controlled several engineer BN.s and sometimes a maintenance company, bridge, truck and light equipment companies. So, there could be cases that an engineer BN from a Corps Engineer GROUP might be assigned directly to a Division for some temporary time period.
TO ILLUSTRATE: my Dad's outfit, the 978th Engineer Maintenance Company was a Ninth US Army unit, attached to the 1104th Engineer Combat Group that was part of the XIXth Corps on the Ninth Army (at that time). As part of the Group, it provided direct support to several infantry Divisions as well as many other support units. During its service the XIXth Corps included several different Infantry and Armored Divisions.
Keep in mind, too, that the person you are looking for many NOT have actually been in the 75th...but was reassigned there for a short period. A number of Divisions were sent home directly from Europe to be reorganized to be sent to the
Pacific...but the war ended before any of them were actually shipped.
Unfortunately, the 75th Infantry Division unofficial history is mostly a photographic history does not provide a list of units attached to it during the war. The history DOES say that the 75th entered combat in December 1944.
I would look up the two books on the 291st Engineer Combat BN:
-----First Across the Rhine: The 291st Engineer Combat Battalion in France, Belgium, and Germany by Col. David E. Pergrin and Eric Hammel (This is written by the commander of the 291st and covers its entire history)
-----THE DAMNED ENGINEERS by Janice Holt Giles.
This book was written by the wife of a 291st member and cover the time during The Battle of the Bulge. She mentioned many members by name and what each Company of the BN did at the time.
These books should give you a lot of information.