If you are looking at making 300 bhp i would drop your injector size by at least 20 %.

If you want a good idle injector size is critical with the original MS due to its 0.1 ms resolution.

I have had problems with it in the past.

With those big injectors you have you wil probably have idle pulse widths in the region of 1.8 ms (of which 1.2 is opening time). MS will not be able to closed loop very well as it can only change the fuelling by 1/6th (in this case) at a time.

If you go smaller injectors your idle pulse widths will go up allowing more accurate adjustment by the ECU and the closed loop will work well.