With a rod bolt stretch gauge. It's hard to see there but you can see it laying with the rods up above.
Basically I bolted each rod in the vise and tightened the bolts in stages until I got the stretch I was looking for (.005"). Then I wrote down that number (which was 55 ft-lbs for all of them). As I installed each rod I zeroed the stretch gauge, took it off, then torqued the bolts to the number I wrote down. I checked them with the gauge after and if they were not torqued enough I loosened them and tightened again to a slightly higher number.