Here are a list of engineer units that took part in the Normandy invasion. As you can see it is very, very extensive. I don't think that people realize the scope of the operation for D-Day. These are JUST ENGINEER units, period. It kind of brings things to focus.
Of course we would have to go in and eliminate units and narrow it down to just those who landed on Omaha for you. But as you can see, it would be helpful to have a bit more info, even a patch or something to go on... 
Divisional Units
1st Engineer Combat Battalion - 1st Inf Div
121st Engineer Combat Battalion - 29th Inf Div
4th Engineer Battalion - 4th Inf Div
307th Airborne Engineer Battalion - 82nd Airborne Div
315th Engineer Battalion - 90th Inf Div
326th Airborne Engineer Battalion - 101st Airborne Div
Here are the non-divisional units...
HHC, 5th Engineer Special Brigade
HHC, 6th Engineer Special Brigade
20th Engineer Combat Battalion
37th Engineer Combat Battalion
38th Engineer General Service Regiment (less Band)
49th Engineer Combat Battalion
112th Engineer Combat Battalion
149th Engineer Combat Battalion
234th Engineer Combat Battalion
237th Engineer Combat Battalion
238th Engineer Combat Battalion
254th Engineer Combat Battalion
299th Engineer Combat Battalion
336th Engineer Combat Battalion
348th Engineer Combat Battalion
502d Engineer Light Ponton Company
503d Engineer Light Ponton Company
531st Engineer Shore Regiment
582d Engineer Dump Truck Company
602d Engineer Camouflage Battalion
610th Engineer Light Equipment Company
612th Engineer Light Equipment Company
819th Engineer Aviation Battalion
991st Engineer Treadway Bridge Company
992d Engineer Treadway Bridge Company
996th Engineer Treadway Bridge Company
RHC, 1106th Engineer Combat Group
HHC, 1121st Engineer Combat Group
HHC, 1171st Engineer Combat Group
1219th Engineer Fire Fighting Platoon
1340th Engineer Combat Battalion
1605th Engineer Map Depot Detachment
2013th Engineer Fire Fighting Platoon
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This list identifies Army units that were awarded assault landing credit for the Normandy invasion, 6 and 7 June 1944. It includes all units except for platoons and detachments that were a part of larger organizations and is based on the following War Department and Department of the Army General Orders: WD GO 70, 1945; WD GO 75, 1945; WD GO 116, 1946; DA GO 23, 1947; DA GO 72, 1948; DA GO 6, 1950; DA GO 37, 1950; DA GO 32, 1953; and DA GO 28 1956.
Proud Daughter of Walter (Monday) Poniedzialek
540th Engineer Combat Regiment, 2833rd Bn, H&S Co, 4th Platoon
There's "No Bridge Too Far"