Hi. Not familiar with uuu but quite familiar with low level things on kobos a few years ago. Hope these things are still relevant.
Based on the pmos wiki you linked it seems that uboot environment is at offset 768, so it is safe to assume that uboot goes first, from 0 up to 768.
I would try to boot that uboot from the backup you already have, just make a copy with the first chunks:
Code:
dd if=backup.img of=uboot.img bs=128k count=6
and try to load that with uuu
Code:
uuu -b spl uboot.img
You don't need to care about u-boot enviroment at this point, it will use the one that's compiled in case it fails to load it from disk.