Stock Rod Limitations?

In a 360 , I'd be more worried about the stock crank going south before the rods will.
If you had them out and replaced them with stock bolts , that was a mis step.
Buy the best bolts you can get and if you want to get really jazzy , grind the forging lines smooth and have them shot peened........these would stand up to a lot more power than a cast crank..........but after balancing and re-sizing , you are getting close to aftermarket rod prices.
And the cast cranks have stood up to some pretty fair power levels considering.
I'd get nervous much over 500 if you could get it in by 6,200 or so.
As stated , the heavy pistons are the real killer in these deals.
But a light slug and good balancing will let these suckers sing pretty good.