get a S5 Jspec with harness and ecu... The ecu is mounted in the same place on JDM and US spec cars. the transmission and engine will bolt in with little problem. Remember you are gonna need a TII hood or to move the intercooler as they have a stock top mount. The fuel pump should be upgraded as the stock NA fuel pump does not flow as much as a TII unit and with simple bolt ons you would reach the limit of it (stock NA fuel pump). The only other obstacle I can see you having to handle is whether to get a TII rear end or a custom/modified driveshaft to go from the TII transmission to the NA rear end. Also, remember you dont know how the motor was treated before you got it. It could last years, or merely a single month, just some food for thought. Ask me if you have any more questions and ill do my best to answer them.

- Chris