I agree with Addo.
I have two cast iron heads, one is on my 67 coupe, the other sitting on a shelf. Considering the 67 is a show car and was built for the purpose of displaying my products, it only makes sense to install the aluminum head, which I'll be doing sometime this spring.
However, I'm not sure I want to sell either one. Someday they'll be a collectors item, maybe not here but definitely in AU. Especially for those restoring a Falcon to its original condition. Hence, I believe they're going to go up in value, rather than down.
The one on my 67 only has about 100 miles on it since the rebuild. It has custom Manley stainless steel valves, hardened seats, dual springs, and teflon seals. It's also has a mild port and polish. The 2V intake is in excellent condition and has been ceramic coated, and has a new Holley 350cfm sitting on it. I figure the combo is worth $1450-1500.
The other is freshly rebuilt with hardened seats, oversized SI stainless valves, single springs with dampers, and teflon seals. However, it has a triple SU intake with the carbs and linkage, which makes it worth considerably more. I'm not sure what it worth nowdays but I'd guess at least $2200, and its only going to go up in value due to its rarity. I've turned down several offers on the intake and carbs, as I won't sell them seperately.
If you purchase a used head, you'll need to install hardened seats, new valves, springs, seals, and a carb adaptor. Plus labor, your going to have at least $1200 in it. Therefore I don't see anyone selling thier iron head and intake for less than $1100-1200, unless they are hard up for cash and willing to take a loss.