Given the spark plug design change and thermostat sitting where it should be;
Thinkin' about going to the yard to pull some heads off an '07 and have them ported so that way I can slap them on in the foreseeable future. Guess anything is possible, but what hardware is needed to carry over/changes need to be made to the '05?
If there's a past thread about this anyone wanna link?
The newer one-piece spark plugs appeared on engines built from 1st December 2007 onwards (basically a mid-year change). Therefore you'll want the heads from a mid-2008 to 2010 3V. It's a plug n' play conversion and this is the list of parts you'll need:
'08.5-'10 cylinder heads
Head changing kit M-6067-3V46
12mm OEM spark plugs
Brown OEM coils (you may be able to reuse yours but not sure if they'd fit)
'07-'10 coolant crossover
192*F OEM thermostat
Gaskets for crossover & thermostat housing
'07-'10 alternator mounting bracket 7R3Z10153A
Upper & lower radiator hoses (only two instead of six on '07-'10).
I've been gathering the parts for several months to do the later coolant crossover conversion with built in thermostat housing. It'll certainly declutter the front of the engine by getting rid of the remote thermostat housing that came on '05-'06 models with all the extra hoses. The thermostat itself, however, is exactly the same from '05-'10.
I'm also toying with the idea of buying a pair of later heads and porting them myself. I've ported the heads on my previous two cars ('92 Jeep XJ & '95 Mustang GT) so I'm comfortable doing it. However I'm only considering it purely for the performance/efficiency gains and not because I'm worried about my existing spark plugs breaking if I try to extract them (they only have 35k miles on them anyway).
Edit: Luckily the 4.6/5.4 3V heads can also be found in F-150s, Explorers, and Mercury Mountaineers of similar age so finding a good pair (or even a complete engine) shouldn't be too difficult.