Suprises under the valve covers - 4v windsor heads?? (links to pics)

Study all the different parts# books, Ford Performance by Pat Ganahl, The Ford High Performance Parts Interchange by Goerge Reid, Ford's Official 5.0 Mustang book by Al Kirschenbaum ( put out by Ford Racing) And lots of hands on experience over the last 30 years, to weed out the mistakes in the aforementioned books. The only one of the above that I DO rely on 99% is the Ford 5.0 book above, the info in it came straight from Ford. The other two DO have mistakes in them, but overall much of the info in them is useful. There are other books too that I've read, but can't recall them off hand.
 
The later 66 heads had rail rockers instead of the slot-thru-the-head to guide the pushrods and keep the rocker tips on the valves. One book I have lists the 289 Hi-po as having that casting # on the block. If you can check, might be a nice surprise to have the block. They had thicker main caps than the others.
 
You can tell where the parts were cast, but as for assembly, that's a little harder to determine. Most I've heard were assembled at the Cleveland plant. Most likey the block and heads were cast at the Dearborn Iron Foundry ( DIF cast into the block)