Taking shorter routes should be left to experts. I erased both disks, made new partitions (under a better scheme than before), configured raid1 with ext3 throughout, and everything went on smoothly for amd64 etch.
I got more than I wanted, booting now ends to gnome windows manager. I assume that Ctrl-Backspace gives me the console with (according to top) little engaged memory.
Anyway I would like to remove gnome completely, replacing it perhaps with jwm (or not replacing).
/lib32 is present alongside /lib64. I lost any hope to get rid of 32bit libraries, so that, unless a useful suggestion arrives how to get rid of them for ever, I leave them. I know that, if purged, they reappear at the next update/upgrade.
Weird. I'm running amd64 without /lib32 and "apt-file search /lib32" says that "libc6-i386" is the only package that install anything there.