Loose belts vs assault pouches
For years I read about how US soldiers complained that their standard way of carrying belts loose or in hard packs was problematic and that they should get a soft assault pouch like the British and Israelis used.
As a former part-time magist myself, I think that carrying belts loosly is sloppy when you are on the move and will cause jams. Belts are better for sustained firing positions. I would keep a single pouch on the gun and the rest of the ammo as belts. For quick reloads you can run the belt over the pouch and then stuff the belt in the slit/flap on the pouch if you have to move again soon
M240B "improvements
Most of the M240B additions add no real utility to the original MAG58 and just extra weight. I read several times of American soldiers complaining about it. Fact is that the USMC, which seems to be a little more sensible than the US Army, uses the M240G model which is almost the same as ours except it has the shorter flash suppressor.
http://www.lejeune.usmc.mil/soi/images/2.jpg
The only thing that I would add is a front hand guard - not like in the M240B, but in the place where the soldier is holding it here:
. This would make it easier to lift a hot gun in order to change positions, not necessarily for shooting. I used to think about creating one from an extra galil handguard
Of course a picatinny rail adaoptor on the top cover is a good idea. Maybe with the price of metals these days, they can finally take the unused SLS adaptor bracket off all the thousands of IDF MAGs and use the profits to pay for it.