You could do it with one of the G5's in FireWire target disk mode...
But you'd need a 6pin or 9pin regular FW cable.
I personally can think of two options.
1. Mount the drive in which the copy of the first hard drive will go to inside of the 2.7gHZ G5's case. There is room for two hard drives in there. See Link for Help
Once it is installed, simply boot off of your Mac OS Install media (CD, DVD, USB) it can be any version that supports the PowerPC platform. You need to boot holding the "C" key. Then choose Disk Utility and hit the restore tab. Drag the old partition to the "Source" field and the new hard drive to the "destination" field.
2. Put the second hard drive into the second (idle) G5. You will need a copy of the Mac OS install DVD as again you cannot clone a drive when it is in use (running the operating system). Hold down the "T" key at boot up and then a firewire logo will bounce on the monitor. then plug the cable into the 2.7 g5 and start it up
I hope that this is helpful.
Long Live the PowerPC G5
Michael K. Moore Jr. wrote:
Maybe I'm not reading your post quite correctly, unless what you state there applies only to cloning via Apple's Disk Utility, in which case I was not aware of it.
I routinely—several times per week—use SuperDuper to clone my main boot HD to make an identical bootable backup volume on an external FW drive using the copy of SuperDuper that is installed on said boot (main) volume while booted off the same, and I always have an identical, up-to-date clone volume.
If I'm somehow wrong on this, I'd appreciate being corrected by any one reading this post.