I was measuring up the 14x6 Tasmans that I purchased to go under the FE. By my measurements the diff (drum to drum) is 1440mm. To centre the rims in the wheel well they need to come in about 25-30mm (1 inch) each side. Is there a holden diff (banjos are OK) that is around 1380-1390mm wide?
Maybe try a banjo diff out if an LC/LJ. I know that these diffs are shorter than FE to HR, but how much shorter I don't know.
This might be your best shot. Let me know how it goes.
Air-chief.
i have an LJ diff in my FC Van and they are 1" shorter each side ;)