I have had a couple of EF's in the past and like the shape etc.
What I want to know is how hard to put a 5.4 into one.

Depends what you mean by hard?
The engine bay is wide enough. Bonnet clearance may be an issue. If you have an EF kickin around I have a 2V V10 we can try for size. I've tried it in my old XG van and it was certainly possible but an E-series has a bigger bay. I've also tried my 390 on an E-series K-member and that was no worries and it has near as dammit the same deck height as a 5.4/6.8.
I'm in Perth too.

Cheers,
Pete.