360 head porting for big power (500HP ?)

Some simple questions for anyone 'in the know'?
Valve choice for J heads?
Tulip or Stainless flatties...
I got Milodon, Ferrea, cheapo chinese and good old 'factory Tulips' as its spring lol.

I can't go to 'all out' portwork, LIKE SKREWS, but how far can you go, around the original guide boss???

Thanks from the Limey

Can't go wrong with Ferrea. Don't use the factory style tulip valves.