But Capecodder told you the Sugino Mighty has a Campy taper,
which my copies of various Sutherland's manual editions also
state. So you can probably get by with either ISO or JIS,
but http://sheldonbrown.com/bbtaper.html
(This is an excellent link and you ought to bookmark it if
you plan on doing this very much in the future.)

There are also pages of charts and explanations in Sutherland's
that are too detailed to post here, suffice it to say i think that if
you are dead set on simply finding a spindle that will work
with your current loose ball cups and take your Mighty
cranks, you will need some luck and a box of candidates
from which to choose.......like at a bike coop or other
vintage parts place. There are bearing race width issues,
bearing size issues, cup and spindle compatibility issues,
issues with where the bearings actually ride between the
spindle cones and the cup races........muy problemas, amigo.

Were I doing this conversion, I'd probably just go with a
sealed unit and some sort of cups for installation similar
to the Phil Wood ones that allow you to move the entire
cartridge side to side by 4-5mm to allow chainline adjustments.

Look here for a photo of all three tapers side by side:

http://www.philwood.com/products/bbhome.php


Look here for a general idea of the sorts of sizes and
tapers and offsets available.......at least from Phil Wood.

http://philwood.com/store/page30.html

This presumes you can invest this much money in your
project and that it is worthy of the investment.

If you have this sort of info, you can sometimes source
the actual unit you buy elsewhere.