Well there are differing opinions on who was the confederate Chief Engineer @ Gettysburg. Some books and Gettysburg Stone Sentinels show Colonel William Proctor Smith as the Chief Engineer.
However JD Petruzzi's books and my Coddington The Gettysburg Campaign book show Samuel R. Johnston as the engineer. So does Trudeau's Gettysburg A Testing of Courage and the Gettysburg.gov website.
Some books and websites actually show both names.
So I am going with
Samuel R. Johnston as my official answer.
I remember asking Scott Hartwig this question during a Gettysburg Battle walk back in the early 2000's. I have always been intrigued by Johnston's Day 2 recon ride to LRT (where did he really go to?) due to the differing opinions. Scott said that Johnston was the Chief Engineer.
https://www.nps.gov/gett/learn/historyculture/anv-orderofbattle.htm
Page 587 in the Coddington book is where he shows only Johnston as the engineer. Who can argue with Coddington?
Page 582 in the Trudeau book is where he shows only Johnston as the engineer.
I could quote many other Gettysburg books and websites but you get my drift from the above. Most show Johnston as our boy.