The finish looks like hard chrome to me, that would explain the hammer and trigger as they were usually matte after Mahovskys or APW did a brushed chrome job. The color looks more like SS than the slightly yellow tint on nickel which is an indicator too.
At any rate it’s a very good finish and a sharp looking revolver.
More reading I did on the S&W forums those two outfits you mentioned were very popular in the 60’s and 70’s with guys sending their pistols to them for refinishing. I took flitz to it and it cleaned up real good. Like you said looks more hard chromed than nickel. If it’s a non factory job which by all indications it is whoever did it did a fantastic job on it. I didn’t get hurt on the price either. Far as the box it’s not the right box it was for model 17-4. I could ask arctic ammo if they could give my number to the guy who had it on consignment. So I can ask them questions about it.