Before re-arranging the hardware, you could probably boot ubuntu from drive 3 initially by using grub64.efi, then if you have ubuntu running is is easier to re-do the grub-pc install for multiple drives.
Originally Posted by desertskymc
Just unpack grub64.efi.gz and put grub64.efi in the root of the Mac OSX partition, rEFIt should show it and boot grub6.efi.
Then from the efi grub command line
will show you if it can find the ubuntu partition.
grub> search /vmlinuz
You can then try booting linux, but you will have to use the correct root=/dev/sdxx
which might be /dev/sdc2 (or it might be sdbx or sday)
but this should confirm that it is booting.
It may need more boot options depending on the ubuntu kernel version.
grub> search --set /vmlinuz
grub> linux /vmlinuz root=/dev/sdc2 video=efifb single
grub> initrd /initrd.img
such as these -