According to SSS no trimming necesary on the newer triggers but without three hands you will need a drift pin. Line everything up, put in the drift pin from back side then use the original pin and push through while pushing out the drift. Put the clip or nut whichever you have on it and then adjust following thier directions.
As for the supposed missing parts I used the original that came off when I took it apart.If I remember correctly that is the thing not mentioned in the instructions.
Hope this helps a little.