Measuring the rod bolt stretch???
I have never heard of anyone doing this.
In any of the data I have ever run across, you can "stretch" bolts when torqueing but never tightened a bolt based on measured bolt stretch. The standard application involving torque stretching required tightening of a fastener to "X" ft.Lb, or inch Lb, then adding an additional fraction of a turn. Have you done something other than this?