Those look like Blue Thunder 4.3 heads.
Brent is right - they are not really appropriate for any normal small block that will really see any street use. The port volumes are huge, and the amount of required custom fabrication would scare the vast majority of guys. They were designed for the professional "Pro-5.0" racing circuit. Big cubes, big RPM, and a lot of boost or spray.
The 4.3 designation refers to the dimension from the gasket surface to the port ceiling - really tall. Go out and measure a "normal" SB F head and the difference will become quite apparent - an engine with these will be nearly big block sized.
It would be a lot of fun to run an appropriate engine with these in a Cobra though.... in a holy $%#%^ sort of way
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Survival Motorsports
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Engine Masters Challenge Entries
91 octane - single 4bbl - mufflers
2008 - 429 cid FE HR - 675HP
2007 - 429 cid FE MR - 659HP
2006 - 434 cid FE MR - 678HP
2005 - 505 cid FE MR - 752HP