I've not looked at it in a few years, but I seem to recall that ash was fairly close to the traditional Bourne syntax.
I don't know if it is helpful to your case, but if you have a script that is bash-specific, it is a good idea to change the magic line from # !/bin/sh to # !/bin/bash That way, if you're running it on non-Linux platforms it will either work or give you a useful error message up front (in the case that bash isn't installed).
Devin