Originally Posted by poopncow
recommend the following:
the drive side cup has a flange, the backside of the flange (touches the BBshell) is the datum. Now pick a measurement, i.e. 8.80mm. Find the spot on the spindle that is 8.80mm on each BB and measure that distance to the datum. If there is a difference between the 2, the chainline when a crank is inserted will be equally affected. Trust me, I do stuff like this in my sleep.
that's similar to what i did when i was trying to determine if my phil wood BB was ISO or JIS:
here.
if it's true that the tapers are the same length but begin and end with different cross sectional dimensions, one should be able to find differences in the cross sections at the spot where the tapers begin (or end). i measured a cross-section of the spindle where the tapers begin on my PW, miche, and shimano BBs and found the PW to be much closer to the miche (ISO) than the shimano (JIS). brent at PW later confirmed that the BB was in fact ISO.