I'm a bit late to the party here, but there's 3 restrictions:
- Throttle plate
- You can file this down to the correct size (I'll measure it at some point) or there's a $30 part you can get on ebay to replace it.
- Intake runner diameter
- These are annoying to get out but can be fixed with a craft knife or replacing them. I haven't done the math to figure out what the correct diameter or length should be.
- Engine capacity
- If you REALLY want to fix this you could do, but you're looking at a lot of money and effort.
The fuel/ignition maps in the ECU are the same as the HO version but the throttle plate restricts you to 66.667% throttle opening.