This is a little late but I found this which may answer how the 38th Engineers were involved with the D-Day invasion. (Sorry if this has been discovered already)
"REGIMENTAL HISTORY
Published in a Memorial Day program in honor of Robert L. Briggs, Roy E. Yeargin, Ed. McDonald, Thomas J. Aversa, Robert J. Bishop, Bernard G. Koch, and Jack Chinnici, on May 30, 1945 in France, by the 38th Engineer General Service Regiment."
" In England the unit was changed to 38th Engineer General Service Regiment. The unit constructed camps and participated in the intensive pre-invasion training (for D-Day). Attached to the 1st Engineer Special Brigade, the regiment was in the invasion forces on the coast of France."
http://home.earthlink.net/~glendaalex/38th.htm
brian