I've always thought that a heavier block, forged steel crank & rods, ceramic rings, S.S. valves, larger radiator, etc. is necessary for dependable service.
Basically a good idea to do much of that however, the Duratec has been fairly impressive in standing up to abuse so far. It has a reasonably strong rib reinforced pressure cast aluminum block & a forged steel crank already but may benefit from some forged rods, low CR forged pistons, and upgraded bearings none of which are cheap. The SVT heads flow very well, valves are stainless but coating them would be a good idea. With the above upgrades, good custom tuning, attention to oil/cooling systems (as well as tranny, differential, & driveshaft upgrades) I would think 350-400 crank HP may be tolerated just fine..
