I shopped around for a rebuildable 428 and it took quite a while to find one. Most of the wrecking yards I called laughed when I told them what I was looking for. I called one and the guy said he'd worked there for 15 years and had never seen one. And I wasn't calling the yards that specialize in late model cars or foreign cars. I called the ones that claimed to specialize in old cars and fords. I finally found one here:
http://www.gillys.com/
I paid $1000 for it. It had never been rebuilt and was complete form the pan to the aircleaner. Of course it wasn't a Cobra Jet but with the availability of after market heads, that didn't concern me.