: Also, my strongback is slightly convex along the length. If I make a mark 2
: inches below the top, like the book describes, isn't that curve in the
: strongback going to be transferred to my forms?

No. Because you are going to make a mark 2 inches down at each end of the strongback and then you are going to use a string between the two points to guarantee a straight line that is independent of the curvature in the strong back.

Just make sure that the greatest distance from the string drawn straight line to the top and bottom of the strong back are not so great that you can't fit the forms on with room to adjust up and down to match the line.

chris