This link should help.http://http://www.zdspb.com/tech/nova/index.html
The trigger set screw holds the trigger rod in the trigger.
Check the nova parts diagram for a better view. The triggers on the nova and super are the same setup.
The safety is held in by a ball and spring that go in from the front of the trigger frame under the trigger guard. The safeties on novas are designed to hold the trigger back, not front.
The set screw behind the trigger holds the trigger valve in. CAUTION there should be 2 set screws stacked on top of each other in this hole you must remove both to get the valve out.