how much nitrous will a stock magnum motor take

Its just a baseline for a safe timing pull, then you tune from there. Most kits are jetted on the richer side & thats what is recommended as a safe starting point, nothing written in stone. Not fare to make a rash statement, you are basically calling most in the nitrous business clueless or dumb because thats what they "still" recommend to this day, & i'm defending some of the best in the business.