I have a general aversion to "Xerox" engineering where peening is concerned because it cannot be expected to produce best results except in instances where component characteristics and service environment closely duplicate those for which the prior-used peening conditions were developed. In your case, however, it appears that your customer is not forthcoming with any useful or helpful information. The prior peening intensity you cited (6N)is not likely to be damaging and could reasonably be expected to be somewhat beneficial even if not optimal. Therefore, it is at least something on which to hang ones hat. I offer two strong caveats: 1. Do not overcover i.e. 100% coverage is plenty. 2. This is a casting, so if you are peening an as-cast surface, ensure that there are no surface defects e.g. cold shuts against which peening cannot be effective.
After all of this I hasten to add that there really is no such thing as an "industry standard" for peening any materials, information such as that in Table 4 of AMS-S-13165 notwithstanding. Peening conditions must be considered as component specific, taking into account material characteristics, component geometry and component operating environmentin particular.
