How much head work is required? I'm currently regretting not getting some whilst I had the valves re-cut and new guides fitted.

Spec is :
6 studded 200 block,
WRC oil squirters,
Wiesco forged pistons,
Farndon std length conrods,
Balanced bottom end
std 2wd head, new valves etc
2wd exhaust manifold
4wd inlet manifold (thinking im going to need a 14mm spacer)
EFR 7064, T4 0.92
Link G4 Xtreme
1000cc EV14's
70mm DBW Throttle
COP
100m thick large tank IC (Airtec)

I think the exhaust manifold, plenum and headwork are my limits of hitting 550 (maybe even 500) other than that the spec is kinda there I think - oh might need cams now too. IIRC there was a pretty much standard escos with 490bhp? (just supporting parts like injectors)