Wow.Just to keep updated, I've tried numerous mentioned things to no avail. I tried a data recovery on my sdcard hoping to find an old backup there but no luck, I also tried a data recovery on /efs but no luck there either.
At this point am I SOL?
I fixed it.
I ran a data recovery on the efs partition and found there was one file that had been deleted during the update. I restored that to /efs, rebooted and reflashed back to the old build based on MC3 with the old modem again rebooted and everything works.
Phew. Not the best way to start a monday, but glad I got it working again.