Hi,
I had this just yesterday. The libraries of the SystemRescueCD are not
64 bits.
So, you have to proceed as follows.
Boot RescueCD with the alternative 64 bit kernel (and select the option
to load all files into memory)
mkdir /oroot
... mount the partition where you installed Gentoo on /oroot
mount --bind /proc /oroot/proc
mount --rbind /dev /oroot/dev
chroot /oroot /bin/bash
env-update
source /etc/profile
... and now you are in business
e.g.
cd /usr/src/linux-????
make menuconfig or oldconfig
make -j8
make install
make modules modules_install
Don't forget to install grub while you are in this chroot environment.
Then, exit from the chroot environment and reboot.
Good luck
