Sorry for the late reply, I didn't have access to my zx6000 workstation until now.
Just to let you know that I've successfully installed Wheezy using the netinst CD on a spare HDD, using default parameters (using entire HDD and one single partition as partition scheme) except for localization of course.
One manual intervention was nevertheless required. During the installation process, the ELILO boot loader installation failed with /usr/sbin/elilo returning error code 1. I've chosen to continue without installing a boot loader and restarted my workstation using the netinst CD in rescue mode to check what was going on. It finally appears that the default /etc/fstab generated during Wheezy installation encompasses an incorrect entry (well, to me, it is incorrect) mounting /dev/sd?1 (/dev/sdb1 in my case) to /boot/efi. I've simply removed this entry, deleted the /boot/efi empty folder created during Wheezy installation and rerun elilo -v to correctly reinstall ELILO and then elilo --efiboot to create the GNU/Debian entry in EFI.
Everything else ran fine.