A stock cast BBC crank and OEM rods can withstand some big Hp, the key is getting a good spin job (internal balance) and using some good ARP rod bolts. Polishing the stock rods beams would be on my list of things to do as well.
NOTE: if you do go with an internal balance you'll have to use a neutral flywheel and balancer.
I had a friend of mine years ago that ran 5.80's in the 1/8 running a ron's toilet bowl injected 468 BBC.
Granted the car was light, only 2400lbs W/ driver.
But it still had all stock internals and a good balance job, I was impressed.
Not that I would go that far with stock internals but that's a pretty good testament of how strong those stock BBC bottem ends can be if prepped right.
Now if you can swing it, I'd upgrade the cast crank with a OEM steel piece, that is if you can still find one, if so it would still be cheaper than going with a all forged set-up and not as hard on the ole wallet.
Goodluck, Cp