You can get by with a slightly different spindle length. It can be a couple of mm longer,
or sometimes you can even get by with shorter, depending on clearances.
ISO Arms on JIS spindles work fine all the time, but it moves your arm and rings
outboard a little bit, thus the chain line moves outboard.
You can't always mount a JIS tapered crank arm on an ISO spindle, but sometimes
you can and it works fine. Every variation from your original usually moves your
chain line a little, sometimes a lot, sometimes too much.
Look here:ISO/J.I.S. Interchangeability
EDIT: If you really want to upgrade and have some cash to drop,
call the people at Phil Wood and ask them what they would recommend.
But you're gonna drop a hundred bucks plus by the time you're done.
Last edited by 3alarmer; 11-21-12 at 11:15 PM.