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 2.6 Pulley/Idler l Airaid l o/r X l 305 NT555R's l Recaros l
04 Azure Blue Mach 1 / 03 Sonic Blue 3.8 / 14 Sterling Grey F150 FX4 402A 5.0 / 11 GT500 R.I.P.