I think Anon has a good point: you need to be really careful about this. There are a lot of things that might break very badly with this unless you can guarantee that

• machine B is definitely down or at least in single-user mode before you start copying anything
• that machine A has not gotten corrupted somehow, as you'll then break every machine in your setup
• there are going to be a lot of unique-to-the-machine files that are going to be (and should be) out of sync

You may be better off comparing the output from whatever system management you're using (dpkg, rpm, etc.) to a "standard setup" file on each machine; it can check itself and update as appropriate.