they have full port job, bigger valves and 1.6 rockers

 

Ok, they are still not enough for a 408. Those might work on a 347 for a mild build

 

I would go with at least a 205 afr head for a 408

I know what you are thinking when you think it will work. Ford put those turbo swirl heads on the 393s and got somewhere around 430 at the flywheel. Look at it this way though, with a good head you are seeing at least a 100+ hp gain.