Turns out the E3 does obey the same sort of PBL format as the E2, but there's some sort of timing issue with pblq I think. I've hacked up something that does the job and rewritten my boot parameters to drop to /bin/sh and I'm in! Some files from /proc can be seen at:
http://www.earth.li/~noodles/files/delta-proc.txt
J.