With so many other good brands of heads out there why the ford racing Z heads,also you may have to use different headers with the Z heads, I know I had to, the exhaust ports were a different height, if I could do it all over again I would not buy anything with the ford racing name on it, the Z heads on my 427 crate engine had soft valve springs and soft valve guides and was a brand new engine, smoked like a chimney stack from the very first start up, check thread below.
cheers chris.
Ford Racing 427 burning oil