The best way to gain HP without boosting is doing head work.  Check out Exile Racing, If you know your way around under the hood.  If you not think but know you can remove your head and reinstall it while get your timing set back, then I would recommend getting your head port and polished, a 3 or 5 angle valve job and port matching your intake ports.  It would run you around $400.00.  Performance cam would help too but that would up your cost.