I see you've got an Si, Sebring do a good bolt-on backbox for the 1.4 engines, check out their website.
It's worth noting that the Janspeed backbox is only a direct fit for the GTi and you'd need the GTi midsection for it to fit. The good news however is that the GTi midsection will go straight on to your car, giving you a bit of extra power as it's slightly larger, and then you can put the Janspeed one onto that.