This is my first build and am wondering if there are certain receivers that work better with the polish underfolder design?  Mostly I am am concerned about the rear trunnion.  

Let me have opinions on the best trigger groups, gas pistons, etc.  I am not intimately familiar with any of the brands or suppliers

Between people I know and my brother we have 3 or 4 that need built.  Reputable builders reply quote me a price and we may just have them built.

^Thanks a lot everyone

I heard Dan's ammo is good here is a link in a forum
http://www.ak47.net/forums/topic.html?b=4&f=95&t=74054

bump

Best receiver so far is the 1.0mm GT with the ORF pistol grip reinforcement plate added.

I use Tapco G2 double hook trigger sets exclusively - best for the money I have found.

I don't change the gas piston from the one the kit came with - there's better parts to change for compliance.