It is hard to say because I do not think anyone has dynoed just those mods alone. On a modded 98 SVT (single Extrude Honed UIM & 32mm LIM), a change to the later dual Extrude Honed UIM + 34mm LIM netted about 4 HP. So you could GUESS it might get a bigger improvement on a non SVT (no Extrude Hone UIM and 30.5mm LIM) IF it had the same other mods.
Condition of your engine, other mods, your A/F ratio..all unknown but important variables. If you can get one at a good price used..say $350-$400 for the set it might be a good move but I would suggest Y-pipe, catback, intake first.
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