This is the trigger I used:
http://www.brownells.com/rifle-parts...8.aspx?ttver=2
ALG Defense Trigger. I think it took something like 20 minutes to swap it out and yes, I kept the spring for the 5.45x39 surplus ammo in there. I guess that means I've got two extra .223/5.56 springs laying around in my box of treats but who knows? Maybe I can incorporate them into my next build!