I don't know much about V8's but I still don't get you guys?
You have 4.6L to work with...
If you want 400bhp N/A:
I agree on the 4v route, swap to 4v.
Change comp ratio, 10.5:1 should be ok.
Get new After market EFI and Ignition.
Some agressive cams.
New headers and exhaust.
Check the...