A genuine 550-600 hp engine built right. IMO (and this is IMO only, sure there are a myriad of ways of achieving it) I'd go for something like this:

200 block 10 studded with liners (or one of the new ally blocks from Geoff Page if the bugdet allows - prob not )
CP pistons
2.2 stroker crank
hart inlet
spec-r cooler
twinscroll manifold with BW turbo
3.5" exhaust
Management to suit tuner
Plus supporting breather, injectors, etc - guess you already have most of these.
6 degree beam

Essentially the best bits which should be able to go well beyond 550-600 but therefore won't be stressed and fail quickly or be a cause of worry.

I'd also change those bloody wheels but certainly not for comp's - other wheels for fords do exist