Simon, Both the caps and rods should not rock when their joint faces are placed on a flat surface. The side of the big end and small end eyes are machined at the same time, so should be in the same plane, the flat surface check again, a simple test for twisting. The bearing locating cutouts can suffer fretting from loose shells.
The two rods on a single pin trick, thanks Vincent, does the check for bending. A nicely polished rod removes the likely starting points for failure, and is satisfying to do as well as going some way to matching the rods for weight.
The rods should weigh more or less the same, you are lucky if they match exactly with an unknown engine. The damage to the side of one of the big end eyes looks like a sign of some harsh treatment, so as bergs says, check for ovality. Standard eye size for a big journal crank is 1.8435"/1.8440"
Swarfy.