Edited my post to correct my statement, I don't think there's an off the shelf mani that will fit the rules for ST. Looks like your only other options are a grounding kit, running some copper spark plugs, and swapping out pulleys for some underdrive ones. It is debateable if any of these will give you any real power though.
Parking Lot Hero
2008 WRX daily driver
2003 ZX3 23D Autox Car 42 FSP
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