It seems likely that we will be able to switch to SL5 amd64 soon; to maintain compatibility with older versions of BOSS, we'll install 32-bit compatibility libraries.
Using urt, net has agreed to support a custom-compiled install of GCC 4.3.2. I've written a build script for it, and have spent a bit of time refining it in order to make this possible.
In theory, this is Derrick-safe material; if there are issues, though, I'm not sure Derrick has the background to effectively obtain help. Then again, in such a situation, I'm not sure net would have enough free time to tinker with it. I think we just have to hope that there aren't any drastic changes.
With Derrick's fix, the broken symlinks are exactly:
lcg/external/{clhep,oracle,Grid}
The reason these can't also be automatically fixed is because these directories just don't exist here: Alexey is not distributing the clhep, oracle, or Grid packages.