First off u can use the same ecu if you get it reflashed. Second you can use a si motor with ur transmission but si is still a single cam unless ur talking about 99-00 si then thats b series. You have to buy new stuff and modify the engine harness you have to run like 3 more wires. If I was you I would drop a gsr in it thats my favorite b series stock I like all motor better then turbo its just what you like and what your going to do like autocross, straight drag, touge, street courses or just stupid on the street. There is alot of options just do what you like. if you don't know research and find a motor you like