Pretty good stuff, but "old school". In particular 69-70 heads were prized because unlike all other 351W heads, they aren't drilled out for the Thermactor ports. This means they can be ported out a bit better. They enjoyed popularity among certain racers because they had larger valves. In some race classes the racers could pass them off as "stock" 302/351W heads and not be caught until the engine was torn down for inspection.
Some people set great importance by appearing stock while having "a little extra help" on the inside. Personally, give me a choice between a pair of fully tricked out C9OE heads and some "ot of the box" aluminum AFR heads for equal money and I'll take the AFR's every time. (Or TrickFlows, or whatever)
That said...Not caring to invest that much in an engine for my old F150, I picked up a pair of decent 70 351W heads for $50. Ported the heck out of them and like them very much, thank you.
11. If thou be not absolutely sure of thy facts, thou shalt Google before posting thine answer.