the blocker pin is for the 4th gear lock out, if your running a 3 speed you dont have a 4th position. the other pin iirc is because the spacing on some trans between park and neutral is longer so its a compensator...where it may feel like there is 2 position between park and neutral on the shifter...I just installed one, and ill tell you the directions suck!!! I read it 10 times and fiddled with it until I figured it out.