Hi Egon,
no, you cannot use the C1 image for a U3.
There is a dirty way, but that depends a bit on your linux skills:
- take a C1(+) image and backup the root filesystem
- create a bootable U3 image as desribed in
http://archlinuxarm.org/platforms/armv7 ... /odroid-u3- backup the lib folder from that root filesystem.
- then copy the backed up root filesystem from the C1 to your U3 image
- remove the lib folder from the U3 root filesystem
- copy the backup /lib folder to your U3 image
This should work, but it's not perfect.