The HK roller lock system is totally different from the system used by the AK, the reciver is different, nothing about these guns are interchangable. To do any type of AK to HK conversion would cost far more that the price of a good HK clone.
If you are looking for an HK style rifle try here http://www.vectorarms.com/indexframe.html
You can also find real hks on gun broker, but the real HKs are big bucks today. I kick myself for selling my Hk51 when I did, oh well .308 is too expensive to shoot anyway (not that .223 is much better