The catch there is that the injectors are aimed perpendicular to air flow and you are asking a manifold designed for air to now carry an air/fuel mixture. Will you get equal fuel distribution to all four cylinders with this setup? I would be skeptical about the fuel distribution characteristics of this setup. At full throttle, it should be passable. It might not be great at part throttle and transitions. A better choice would be an extra injector in each runner, aimed in the direction of air flow, and close to the head.
Extra injector systems work pretty well because you can rely on the stock ECU to automatically adjust fuel at lower loads. Of course, at higher loads the stock ECU fights you by trying to lean out what you are adding with the extra injectors. If they fight too much, you can just go to wide open throttle so the stock ECU will stop adjusting. Everything has its pros and cons.
