I didn't do anything to my trigger other then the cut out for the spring.
I modded the disconnector (or wedge) that the trigger pushes against, mine was long and wouldn't reset when you released the trigger.

It might be easier if you could post a pic of yours.
If you look at this thread again at reply 64 I have two clear pics of mine before I modded it, you can see how close the disconnector is to the trigger, and reply 69 has a pic of one that has a gap between the diconnector & trigger.
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I also came across this, Pirate is mentioning how to fit them together, don't know if it will help or not.
http://www.gunco.net/forums/f294/semi-rpd-fcg-60221/



And that's a nice tut that guy put together, thanks for posting it, he explains it well too. And yes it looks like he mainly just polished the parts.
Also if you go down near the bottom of that tut link, the pic above the video shows his FCG installed. You can see how he has a small gap between the trigger and disconnector, mine didn't have this and that's what I had to mod on mine to get it to function.