Just picked up my 6.0 block from the machine shop, bored.030 over,hot tanked new cam bearings. They removed two small soft plugs and they couldn't remember where they came from. It sat for a long time waiting for a special thread chaser to come from ARP. I think they go in the oil galley, front & rear but not sure, anyone know for sure? also the little plastic piston not sure about that either???

 

sounds like the oil galley plugs, one should be behind each cover, front and rear.

 

When you say "little plastic piston" you might be referring to the oil gallery plug(looks like a tiny barbell). It plugs the oil gallery at the rear of the block. The "O" ring goes to the outside.

 

Yes thats it. There's no o ring though. Does it go in the galley then the soft plug seals it?

 

Yes there is an O-ring on the oil galley plugs.

Take a look at this page about the 6th picture down. Looks like a dumbbell with an O-ring.
http://www.automotiverebuilder.com/ar/eb040538.htm

 

and yes they go in one way.
check before you install them and not put them in backwards.

 

Thanks Guys..................................