Do you already have the hyper pistons or are you trying to decide what pistons to get? They should be ok under a small shot like a 125 but if you are rebuilding right now it is worth the couple hundred extra bucks to just get the forged.
yea i got the stuff for a deal ! With hypers allready in the mix, maby a good tune they will last but very little room for error is what ive found. Any real world experience applical here!
I haven't ever run nitrous on a 347 with hypers but I have sprayed a 100 shot on my 93 plenty of times. It came from the factory with the hyper pistons in it so I would imagine that you will be fine. Just don't get greedy, I would go 125 at the highest, and if at the first sign of detonation get out of it and you should be fine.