Whatever you do do NOT remove the heads!
Youll only find tons of cracks in the valve seats and want to replace them...
Dont ask me how i know:-)
It sucks as the magnum heads look so much better than la heads.
Im positive a very small amount of porting/clean up will make them flow very well.
But they all seem to have cracks and throwing time and money on cracked heads is hard to motivate.