Ive been iffy about the stock rods with my 836 build. The one thing i never hear anyone talk about is shot peening the stock rods. I cant seem to find much data on how much strength it would add but i do know its an old trick with muscle cars to get just a little more out of the rods..
At the time, it was either RC Engineering or ACtion 4s or both + others, that did shot peening, heat treating, and big bolts. The claim back then was unbreakable. Until they started makinng forged and/or alloy, and they were unbreakable, etc.
The stock rods can be made pretty strong for most uses except Turbo or such. But RR is right in wanting to crack test them. I had a bunch of parts magnafluxed and it wasn't cheap. Due to the small lot mainly.
Seems to lean towards some CycleX (or APE?) rods for cost effectiveness.
You could cryogenic treat them cheap but still doesn't answer the crack question.