I use this gauge. You have to wiggle it around a little to find your number. I measured a few rod bolt lengths and made a standard with drilled ends that mimic the bolt divets. This standard is marked top/bottom. Set the gauge to zero on the standard. Measure all the bolts 1st. Then you will know how they compare. Some will be longer, some shorter. Add you stretch figure to the measured numbers. Write all the measurements down keeping track of each bolts rod location in or out. So for example; say rod #1 inner bolt measures + .0005 and the outer is -.0006 vs the std. Lets say the spec is .0060-.0064. Now when you measure after stretching the inner should measure .0069-.0073 The outer should be .0054-.0058, This way you don't zero the gauge everytime. You can go back to your standard at anytime to check zero.
Doug