Im looking at 74 and 47 gas pistons and I dont see any difference between them.  Am I wrong?

IIRC, shouldn't matter, after all, it's an AK .  AFAIK, the only different parts that can't be interchanged are forward trunnions, barrels, bolts, bolt carriers (I think), magazines, bullet guides and ejectors (A -74 ejector can be used to make a -47, not vice versa).  The gas port size is different, too.  Full-length AK's generally share the same gas pistons while the shorter ones (Krinks, etc) use a shorter piston.  

Quoted: IIRC, shouldn't matter, after all, it's an AK .  AFAIK, the only different parts that can't be interchanged are forward trunnions, barrels, bolts, bolt carriers (I think), magazines, bullet guides and ejectors (A -74 ejector can be used to make a -47, not vice versa).  The gas port size is different, too.  Full-length AK's generally share the same gas pistons while the shorter ones (Krinks, etc) use a shorter piston.

Yep pistons are pretty much interchangable

www.MidwestArmory.com

If I remember correctly, the 74 piston is usually a little shorter than the 47 piston but both will work.