It's HK94 (9mm) stock. I know that few old HK53 came with like the ones on MP5, but still inteaded for .223.
I know that I am not 'suppost to' use HK94 stock on .223 HK93, but after some research I came to conclusion that there will be no major difference between plastic buffer of HK94 and spring loaded metal buffer of HK93-A3 stock.
I heard several people uses HK94 stock on their 93/33, and they all say they haven't experienced any problems. Though opinions may differ.
The old concave A3 stock is uncomfortable, and the new version looks aweful in my opinion.
The plastic lower is awesome, though not as comfortable as finger grooved factory grip, the narrow grip makes controls more accessible. You can actually release the right side safety with your index finger.
Also, the non-slip textured grip let you hold the grip more firmly. I can actually shoot the thing one-handed now.