i would probably pass on that, the heads off of a cobra are iron, a new set of gt40 aluminum can be purchased for around 600 a set the are lighter and you have the option of different combustion chamber sizes, if you can get them for around 200 and sell them on ebay to some one who will see "cobra" heads and you might make 100 bucks off of them. the gt4o aluminums will out flow the stock cobra irons as well.
look in the back of any musle mustang and fast ford magazines or search the web many places offer "take off" gt40s wich were removed from ford crate motors. usualy start around 600
profesional products also offer heads modled after the performer rpm seris for relativly cheap, pro top line and other companys offer low priced heads that will more than likley out flow the gt40's, it just depends on your budget, IMO if i were to spend money on new cylinder heads i would not spend it on iron.
P heads go for cheaper around 300 because it costs money for the headers, theirs not a big demand for them at a high price if you have to buy headers also. I got my gt40p heads on corral, valve job, new springs, scorpion 1.6rr's for 290, picked them up local...
Im in winter springs florida, ill sell you a set of gt40 non p heads for $350, you can pick them up.