The C9OE and D0OE were some of the best factory head castings of their time, as has already been pointed out.
These 351W heads were incredibly popular as a low-buck high performance head to use on 289's and 302's. The small block ford performance cylinder head market used to be non-existent, now...you can get a high performance small block ford head from dozens of different manufacturers. When there was a real lack in aftermarket SBF heads, the C9OE and D0OE heads were the ****.
The downside of the larger combustion chambers of these 351W heads, and thus reduced compression on a 289 or 302, was offset by the fact that these heads came with bigger valves. The valve sizes on these 351W heads were 1.84"/1.54", which was larger than the early 289/302 heads' valves (1.78/1.45) but obviously no bigger than a "3-bar" iron gt-40 head.
The intake ports on the 351W heads were also wider, measuring 1.94" x 1.16" versus the 289/302 1.94"/1.04".
To make up for their bigger combustion chamber, most people who ran the 351W heads on a 289/302 milled the heads by .040", which reduced the size of the combustion chambers about 7cc. If you milled the heads by .040 to raise compression, you also had to mill the intake manifold mating surface by .057" to properly realign the intake manifold passageways.
Since these heads were mostly used on fairly high revving small blocks, it was recommended to remove the press in studs and replace with screw in studs and guide plates (Ford guide plates were stamped C9OX-B).
If people really wanted to get the most out of these 351W heads, it was popular to install a set of GT-40 valves (old school). These valves were slightly larger than stock, at 1.875"/1.625". The valve seats have to be reworked to use these valves. The intake valve needed a 60 degree seat, and the exhaust valve seat needed to be set to 45 degrees.
