How much you can deck the stock head is going to depend on cam choice.
Stock cam you can take quite a bit and be rather safe on 91/93.
Any aftermarket cam and you should deck less just to be safe.
If it does happen you get knock you can swap to the SVT head gasket being it's thicker.
The ZX2 guys (John P) has safely taken 0.090" off a head. IIRC I'd measured the extreme end to be 0.120", deck to highest point of the valve seat.
The intake side becomes restricted by cam choice and valve diameter. Look into what a Ford Racing head looks like, try to mimic it.
On the exhaust side, it's very restrictive. You can open them up quite a bit and gain a fair amount of usable power. The key here is surface finish (no matter what anyone else says). The smoother you can get the entire port the better, reduce surface area, increase flow and decrease heat loss which keeps velocity up.
Stock cams/valves, you'll start to choke around 6,500rpm. Porting won't change this much.
Big valves, cams and porting and you can extend the RPM range a fair amount. 7,000+ isn't to hard to do. And then you'll start to see the kind of HP #'s you're thinking you'll get.
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