I think you'd be lucky to see 350-380 rwhp after cams, ported intake, head work (though the c heads are just fine imo), and all the usual bolt ons.
It'd be much easier and cheaper to run a low boost centri application and some 4.10's for a solid 400+ street car.
Do some digging on the registry or SVT
performance, majority of guys looking for 400rwhp are opting for FI of some type. A couple guys have gone the n/a route but I believe they spent more to achieve a naturally aspirated 400hp than the guys going FI and seeing 500hp with some coin left for suspension etc.
12 Black GT500 SVT PP l VMP TVS l JLT123 l O/R X l 28x11.50Rx15 M/T Street R's l BMR Suspension l Recaros
03 Sonic Blue 3.8 / 17 Magnetic Fusion Sport 2.7 EB