Tracking differences between Gentoo-x86 and Gentoo-ppc

[notClown]

Hello,

I'm currently running Gentoo x86 on an Athlon box and Yellow Dog Linux 2.2 on an Apple iBook. However, I might be interested in running Gentoo-ppc on the iBook someday (when I have time). While some have criticized Gentoo for being "only for broadband users," it seems to me that keeping both systems up-to-date and backed up would actually require significantly *less* bandwidth if I only had to keep one set of sources around, with some patch files and different .ebuilds making up the difference between the two architectures.

So here's my question: is there any easy way to keep track of the differences? I assume the tarballs in /usr/portage/distfiles are "official" source packages, and any differences in actual source code would be applied as patches. But how might I go about keeping track of what's different between the patches and between the .ebuild files? Or, more significantly, has anybody written a script that might do this kind of thing? I might be able to work on one at some point, but I don't know how flexible it would end up being. Any suggestions would be appreciated.

Thanks!