My gut feeling is that the American Legion stamp probably takes a little off the value, but if all the balls look that nice, they're probably still in the $150 range. I've not seen one with an American Legion stamp for sale before (never looked for one either), but with the Am. Legion not being a pro-level organization (though certainly producing its fair share of pros later on), I think that would be a detractor rather than adding a premium due to scarcity. Since the Legion stamp is on the side panel though, they would still make nice display pieces even if the buyer really would rather not have the additional stamping.
The balls are also early-1950's vintage, so not as early as the one Leon linked to (which, ironically, is being sold by the author of the ball guide that I just looked that info up in).
Again, that is all my conjecture, and others are free to disagree or correct me, but if your buddy wants to sell them at $50 apiece, I'll take all 6
