I just got my first AK, a Romanian from Centerfire, most of the parts look great. Now for my Q, in the rear trunion are there 4 rivets or 2 that go all of the way thru? TIA

2 that go all the way through.

Thanks! Now how do you remove th gas piston & is it left hand thread?

there is a pin that goes through horizontally, where the pistol (right hand thread) screws into the bolt carrier. if you look very closely, you should be able to see it, it may help to sand off the finish. I usually grind on it a little and punch it out halfway, the drill it out I think it takes about a 1/8" bit. the carrier is hardened  steel, harder than a trunnion I think.. after that I vise the piston and unscrew it. IT's easy once you know how.

afterwards find the right size nail to put in there.

My friend just used a 5/32 drill and an AK trunion rivet.

hammer it is there, and file it down to shape.