advance adapter radiator is smallish and expensive, although they did finally re-design it to a 2 core aluminum unit (I have one waiting to go in)
Be Cool radiator would be cheaper, check Summit and jegs once you have your dimensions
4.0L radiator will only fit if you cut apart your radiator support, with the engine driven fan there is no room for a radiator that does not fit uinder the radiator support. Even with 1 or two e fans its going to be TIGHT
Unless you move your engine back more
If I could do it over again I would simply remove the radiator support on my BII and the inner fenders as well, make the hood/grill/fenders/lights, etc all mount on a tube cage.....
that is where my BII is going eventually, so knowing this it would have been easy for me to cut up the stock radiator support and use the 4.0L radiator for the first gen truck..(similar to Rookieshooter) I avoided cutting my truck when I did it, I couldnt see that far in the future, so as you know I went with a $550 Ron Davis radiator that started leaking in 3 months... that radiator is still in my truck, still leaking.... but I will be runnig the advance adapters unit I picked up for a steal soon when I install my new winch....
I have 2 or 3 first gen 4.0L two row /auto trans radiators like new sitting around, I would love to use one of those when I do cut my truck up for ease of replacement.
So the answer is yes you can use the 4.0L radiator if you cut up your core support so it can move far forward.
Also the Gt-40P has a high volume water pump and oil pump according to Ford MS catalog, I guess this is compared to the other pushrod 5.0L's that came in the stangs...when they fit it under the hood of the ex it required all the cooling help they could get = water/filter oil cooler, high volume water pump, etc just my guess