In the near future I'd like to add an Accuracy Speaks single stage firing group to my AR.

Their web site says the "fitting" is require to intall it.

How much and what type of fitting is required?

Thanks!

Fitting the trigger on mine required grinding the trigger tail so the safety would engage. It passed a function check initially but at the range would fire a second round when the trigger was released so I ground the disconnector to increase the engagement. All this needs to be done carefully a little at a  time, so you'll install and test a few times before its right.
Mine is in a Mega Gator lower with a 50 Beowulf upper. It was a very big surprise when it fired the second shot on release but works well now. I believe I performed the initial function tests correctly, but the 12 or so single shots as broke in the barrel probably caused a marginally engaged disconnector to settle in enough to  fire the second shot on release.
Later at home it failed the function check about 75% of the time.