Not so fast Lewis, we need to know if the centerline was pulled from measurements off the deck or off the hull. Reason being, decks can be moved all around the hull flange to make the 2 big parts fit together. Rarely will you see the gaps between the deck flange and the hull flange the same from one side to the other. Since the hull (keel) doesn't change regardless of how the deck fits/shifts/whatever, it is imperative that the centerline location be taken from hull measurements only. While 3/4" is a lot, we still need to know where he took his measurements from.
There are typically 2 ways to find the center, providing the motors aren't hung yet. One is to have a co-worker (or buddy) hold a straight edge up against the hullside. Hold a tape measure against the straight edge, then make a mark that is evidently past the center. Do the same from the other side of the hull, then split the difference. The second way is to securely tape the end of a tape to the chine radius. Hold a pencil securely against the tape an draw an arc such that somewhere in the middle of the arc, it crosses over the "estimated" centerline. Do the same on the other side of the hull, where the 2 arcs intersect is your centerline.
With the engines in the way, obviously determining centerline is much more difficult. A wood block cut into a right triangle with the angle opposite the height of the triangle being the deadrise angle would do it. Hold the block up to the hull such that the very tip of the base if even with the keel, then take a square, align with the base, and draw a line straight up.
