Some aftermarket triggers will drop right in, but some require fitting the finger piece to allow them to travel back and forth smoothly.
That consists of sanding the top and bottom (equal amounts) of the finger piece until it moves freely, but without any slop. A good, hard, flat surface, a sheet of fine sandpaper and PATIENCE are all thats requried.
You can buy either a drop-in or a GS fit trigger. It is not hard to fit a trigger but that really depends on your level of skill. On a GS fit trigger you can remove material with a hand file off the bottom and top of the pad. Then I like to radius the trigger face by reliving the hard edges. Then just to be safe it is recommended to bevel the back of the trigger bow so it can’t touch the sear spring. Depending on the trigger you need to set the over travel, For S80 guns you need to set it so the FP doesn’t crash into the FP block. Since you are going to the trouble to change the trigger you should polish the trigger track, Brownells carries the stones for that job. I like to use the Brownells trigger stirrup to get the bow true. Check for any interference between the bow and magazine and you should have a nice job. This web site can help http://www.blindhogg.com/
I have had good luck with CMC/McCormick triggers in both Springfield Armory and Colt 1911's. They drop right in and function well after adjusting the overtravel set screw. Are they absolutely tight top to bottom? No, but for a home trigger replacement I'd rate them as good. Be careful with the bows, if you bend/distort them at all, you might as well throw away the trigger is you don't have a bow jig to straighten them out! Pay attention to the sear and disconnector positioning if this is your first time taking at 1911 down this far. If you have a series 80 gun, pay particular attention to the firing pin safety. They must come out with the sear and disconnector and are difficult to get aligned when putting everything back together.
Embarassing story about the FP Safety. After working on my USPSA competition gun (Para Ord P16-40), I reassembled it without the FP safety actuator...OOPS. Went down to the range and could figure out why the gun wouldn't fire. Went off a couple times then stopped. I yanked off the slide and immediately found the reason. Why did it fire a couple times? The FP plunger in the slide was so fouled up that it was sticking. The embarassing part was my "flinch" went the gun didn't go boom. Of course, two of my fellow competitors were there practicing too and overheard my cursing and watch my flinching. These are definitely "learning opportunities".