Did you measure the RH spindle extension beyond the fixed cup before taking things apart? if you had, duplicating this measurement would be easy when looking at the new BB. How did you measure the old spindle? Ruler, caliper? End of spindle to other end? The discrepancy between the stamped (115) and your measurement (about 122) makes me wonder what's going on too.

Bring in your spindle and ask the shop to sell you the same and see what that one is before you leave the shop. Bring in your measuring tool too. Also many older loose ball spindles were not symmetrical in the bearing to end lengths. Most modern Bb's use spindles that are symmetrical. So just going by over all length might not get you the chain line you hope for if your old spindle is off set WRT the bearings. Lastly the amount that the arm pulls up on a spindle will be a touch different as the tapers are slightly different from spindle to spindle. This is why Shimano started to use a collar stop sleeve, the arm would butt up against it, insuring a better chain line dimension control. More then a few times a year i find that i remove a BB, after matching it's size with the worn out one, and go to another spindle length to get the crank best positioned.

If you're the installer you should ask the shop their exchange policy before you go ahead. Andy.