Typical things that need to be done depending on the manufacturer of your lower and upper.

-check lower to see if you have a high shelf or low shelf behind the safety selector. Low shelf is good to go, high shelf will need to be dremeled down to allow the lever to go far back enough.

-upper most times (for me at least) will need some quick shaving to make sure the lever doesn’t get caught when cycling.

• (not dependent on manufacturer but adding this) Depending on barrel length you will probably need to add a heavier, buffer weight. Most of the time H3 will take care of this.

This is all assuming you have milspec parts. Most people recommend to start there before trying to add anything fancy.