I used short 8mm screw (matched to YZ screw) Then when I received proper ECU the screw looked way longer. I decided to stick with OEM procedure and it turned out to be major waste of time. You are OK to use short one. I can also give advice about removing stock screw. Unless you have security torx small enough to get there, you will have to struggle. I spent some time wrestling with various plyers and none worked for me. Then I took a chisel with small hammer and gave the bolt light tap around 2 o'clock going counterclockwise. Bingo!