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...Suntour Superbe components were modeled in direct competition with the Campagnolo New Record stuff that was contemporary with it. So initially it had stuff like 144 BCD chainrings, and I do seem to recall ISO spindles as a part of the group. It's not unusual to be able to get them to work on another standard of square taper spindle, but it's not guaranteed.
This is explained very well on Sheldon Brown, here.
The most usual event is that when you mount an ISO socketed crank arm on JIS tapered spindle, it ends up farther out on the spindle. This affects chainline. You have to mount everything and measure to see how much, and in some cases it can be an improvement on what the previous owner's setup was. But If it ends up too far out of line, you need to get a different spindle in there. So at that point, unless you have a big box of spares hanging around, it's just better and easier to order what you really need, as a one piece sealed unit, with Italian threading and shell width/spindle length, online. It's preferable to spending a lot of time futzing around and mounting and dismounting a number of times with different setups.