Explorer intake is a must as thats the biggest restriction to air flow. GT40 heads are not worth the effort and cost for only 30 HP IMHO
You keep throwing a blanket over the GT40/GT40P swap. That is a basic low buck upgrade. I know it is not a phenomenal hp gain, but it worked on the Cobra mustang and helped the explorer gain low end torque to get that mass moving.
That said you can spend the 800-1000 bucks and grab a set of aluminium heads but if you're running stock cam, the gain will be not much more than with iron heads with comparable valve size.
And this is where a plan is needed, basically 'what I am going to do with the car'.
Basic driver: low buck 'I want to pass and keep up with traffic ' not looking to race Honda Accords'.
You need 350hp now to race the majority of factory junk being made now. Once you get to that point you should be sinking some dough into brake upgrades ($$$).
After this point (more than 350hp and other factors start to pile on including driveability, and you are leaning toward a race car.
Of course there are a slew of variables. But to say the GT 40 heads are not worth the effort is BS.
I suggest looking for the SBF head comparison on the Engine Masters show, good info there.
As always you have to watch the money, spending more than a few hundred dollars on iron heads ok, more than that you have to look at options.
If you don't have a plan, backed by research, you likely will be wasting time and money.
Of course this is MY opinion, I can understand the limitations of iron heads and the advantages of aluminium heads and I understand why you have your opinion.