You'll lose torque by putting on a better flowing manifold and stock heads.
The stock manifold is where a lot of tq comes from. It is junk when combined with aftermarket heads.
Kill numerous birds with one stone and invest in this.
Trick Flow 350 HP Twisted Wedge Top-End Engine Kits for Ford 5.0L
Trick Flow does the work, so you don't have to.
Trick Flow 350 HP Twisted Wedge Top-End Engine Kits for Ford 5.0L provide dyno-proven power without the guesswork. Built around Trick Flow's Twisted Wedge Street cylinder heads, the kits include a specially matched hydraulic roller cam, StreetBurner EFI intake manifold, roller rockers, gasket kit, billet timing chain, pushrods, short valve covers, and our billet oil fill kit. Lifters not included.
Summit Racing
TFS-K514-350-370 $2,449.95 
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1995 Forrest Green Mustang GT 1/226 Made
*UPR CAI*, *Pro-M 75mm*, *FRPP 65mm TB w/SVO elbow*, *Extrude Honed GT40 Tubular Intake*, *Extrude Honed GT40 Iron Heads w/multi angle valve job*, *Cobra 1.7's*, *Stock Cam*, *FRPP Stainless Shortys*, *Prochamber*, *Flowmaster Stainless Catback*, *3.73's.*, *Hughes Performance 2500 Converter*, *Performance Automatic AODE*
251RWHP/284RWTQ with a Radical Racing Tune.