Your heads will work fine, but you're much better off getting some aftermarket heads. I'd suggest looking at AFRs if you need street legal heads. Fully CNC machined ports and combustion chamber, higher flow numbers than anybody else (street legal versions that is), customization from AFR available, all aluminum....mmm, aluminuminuminum....yummy.
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Capri306, Moderator, The Mustang Works Online
1979 Mercury Capri, 5.0L -- C4 -- 2.73
1987 Mustang LX Notch