Multi-kernel: Install x86_64 into working i686 system

[carbonti]

Synopsis - Had tried and failed to successfully install x86_64 Gentoo into a dual Xeon EM64T box. My first Gentoo install. Abandoned x86_64 config and successfully installed 32-bit instead. Running OK but I think it is a mistake to CHOST="i686-pc-linux-gnu" with FLAGS="-march=nocona". Also think it is a waste to have 64-bit extensions available in the CPU and not ustilize it.

Therefore, I want to make another attempt at a muti-lib enabled x64_64 Gentoo installation. The only hardware change from the previous failed x86_64 attempt is a change to the MPS version from 1.4 to 1.1 in the BIOS. I hope for a better result this time. I will do the install via stage 1.

Question: Can I simply install 64-bit & 32-bit muti-lib Gentoo into an existing i686 system without clobbering lib and module directories used by the existing i686 install? I would think some segregation of directoty trees is mandatory as the bootstrap.sh will make different gcc/glibc and associated toolkit chain differences in a 64-bit installation. But I don't know the structure of those directories relative to a 32-bit install and if there are conflicts. Do 64-bit lib & module directories get built in their own branch? How can this be done?

I have enough disk space to "dd" 32-bit partitions somewhere else if needed (or make new 64-bit partitions to install into - same thing, right?). The current /, /boot, /usr, /home and /var directories are on different partitions. I would guess that the existing /boot. /home and swap partitions can be used unaltered in a new 64-bit install.

Any and all suggestions or comments are welcome. Thanks in advance for your response.