Couple of things:

1. The most significant factor in determining BB spindle length is the crankset. Different cranksets will have differing amounts of offset and, consequently, will require different BB spindle lengths for the same bike frame.

2. You may be out of luck. I could find only one Power Spline BB in my (old) Quality Book. It's 68 mm X 113 mm. I suspect the 113 mm may match your crankset but I'm guessing from the description of your frame it might require a 73 mm BB.