Those C8's also have lower exhaust ports for the Mustang and Fairlane's tighter engine compartments along with the different bolt pattern. The lower ports don't flow as nice as the C4's higher ones. Everyone's right about spending too much money on the old heads. Just do a valve job, clean them up and use them. Any more than that go to the Edelbrocks, unless you have skills and can do some port work yourself.