I am in a machine shop of a retired racer. So we have all the equipment but it is 30-40 year old stuff not state of the art. I pressed the pins out, cleaned the rods, have a balance beam scale and the correct fixtures for weighing and hanging rods. Not the state of the art stuff, but older. So part of this is hobby learning and doing. My time no cost.

Regardless, the potential to induce an error by summing multiple measurements is greater than a single error on a single measurement (usually). Having measure rods before, my experience has been that measuring both ends never seems to add up to total weight. Even with best effort to be consistent in measurement, level, etc.... For these rods the sum was 4-6 grams different than a measured total.

So I always measure total weight of assembled rod first. Then measure big end. Then inspect why any major anomaly. In this case the heaviest rods had pads that where larger then the 6 rods that were equal in weight. Those two came in nicely with weight reduction of the big end. The problem was the lightest rod had the largest big end weight and its pad looked similar to the other 5 rods of near equal weight. So it had to be a density of the metal issue. When I measured the small end it was smaller then the rest too.

These rods all looked like same batch too. Same group letters and numbers. In this case DF-21 thru 23, and B on opposite side of LY. All the pistons where stock 1970.

I can't really reduce the big end of the lightest rod without driving total way lower. I then would have to reduce small end on all those other rods with out the meat to remove so it would be a spiral effort down.

I do have other rods I can swap in, but more of my curiosity was how critical is this really. How to approach this if you had to use it. Which I think has been answered. Moving rods to try to get pairs matched. Error on small end is less of a factor then big end. Assemble balance weights to account for it. We have that counter weight material too. We have a crank balance machine, unfortunately not fully operable, so final balancing is done by the local machine shop.

I will post where I am at later, left the info at the shop. Thanks for all the replies.