[leegreen]

the concern with going to narrower shoes is the offset of the wheel cylinder, the length of the anchor points and the length of the hold down pins and springs.

You don't want the shoe to sit crooked relative to the backing plate as may happen if the anchor points hold it away from the backing plate,
you don't want the wheel cylinder to bind as the shoe is no longer centered and you don't want the hold downs too long so the shoes rattle.

you can go narrower but it is not just a matter of slapping narrow shoes on, you need to confirm the setup will work properly or replace some parts with those designed for the brake version with narrower shoes.


an aside:
48chev mentioned reducing rear brakes power as one possibly desirable outcome of narrower shoes. Another way to do that is to put on 4 of the front shoes with less lining material or simply sand away some percentage of the surface area of the lining on your existing shoes.
-taking precautions with the dust!-