Thanks for the correction, I couldn't pull PK out of my head yesterday morning. However we both forgot to mention their magazine fed SAW, the RPK series.
I'm not aware of a cloth pouch for 100 rounds of 5.56 linked. They recently have made a minor change to the design of the plastic box. There are now black and green boxes in the system, the black being the new one, but I don't remember what change they made to it. There are good systems in both magazine and belt fed varients. You run into problems when you try to do both in the same weapon. I personally prefer the belt fed systems. But others may have different needs or their logistical tail may support one or the other better.
I'd very much like to see the USMC manual on machine guns. FM 23-67 on the M60 also covers indirect fire but it's just plays lip service to it. I have a good friend who was a GPMG gunner in the Light Infantry of the British Territorial Army and they actually removed the buttstocks of their MAG 58s, mounted a mortar sight and trained in the indirect fire mode. 25 years in the US Army (21 years Infantry and 4 Artillery)and I have never seen this done. Indirect fire was used a lot during WWI but sometime between wars this seemed to go away in our army. I find it interesting that many M2 .50 caliber MGs have the mount for an indirect fire sight on the receiver.