The Mighty (or Superbe) taper is in fact identical to any Campagnolo cartridge bb taper, all are ISO.

What was copied by what and when I have no idea!
But a typical early-70's Stronglight bb taper is small enough to be more similar to ISO than it is to a Campagnolo pre-cartridge bb taper.

When mixing JIS spindle taper with any old Euro crank, expect the crankarms to rest about 2mm further out on each side, with a total increase in "effective" spindle length of perhaps 5mm. It's not a huge difference and it's not anything like 5mm on each side as is sometimes suggested!

When in doubt about spindle taper fitments, usually the most relevent thing to check is the comparitive spindle taper width of the JIS and "other" spindle that is being replaced.


One can also lock their caliper's jaw to the dimension that positions the jaws flush with the end of the wider spindle, and then apply the locked caliper to the smaller spindle to see clearly how much further that the jaws (and hence the crankarms) will slide over the smaller spindle (and vice-versa when the thicker JIS taper is used).

Be aware that when buying a tapered bb assembly that is intended for use in Schwinn/Ashtabula bottom bracket cups that almost all of these heavy units are extremely long, even for a mountainbike with a triple. It makes me wonder what crankset they were intended for, and makes me suspect they were perhaps designed for use around very wide tires.