Gun Surfer:
The little set screw is used only to butt up against the bottom of the receiver and to keep the trigger secure. Don't overdo the tightening, just enough to keep the trigger housing from wobbling.
After installing the trigger, you may not be able to engage the safety easily. You will then have to put a longer bevel on the cocking piece with a medium india stone or (carefully) with a dremel tool. Not as hard as it sounds, so good luck.