Wow...that's a boat load on ponies for a Mustang Ken.
I was told there's lot of meat left in these heads and someone like Chad Speier could likely do some additional porting if someone wanted to chase numbers. I almost went with a big solid roller and a set of 1.6/1.7 shaft rockers but said to myself...be sensible and build it so you can drive it. I plan to run this one mostly in the higher RPM ranges and trust we'll get an honest 400hp from it without too much work.
I'm having fun with it now.