Well shoot. I had to wait until the end of work today to made an edit (however rough it is), and it looks like I just missed posting it in time.
Here it is anyway:
I was going to suggest the same reference you used because it's much more Nurgle.
Bloated stomachs are a dead giveaway that someone is Nurgle. Also hives breaking out of their armour and often guts hanging out. Sores are also common.
They seem to sort of shuffle around like zombies, so too rigid a stance won't make them feel very Nurgle.
Two big things you are lacking though:
Horns/external bones and their breathy backpack things (I think they're used for air ventilation?)
As a side note, all Plague Marines carry a plague knife don't they?
I never got very into playing the game, but I loved my Plague Marines (they are actually Chosen I converted with some greenstuff) and I really like painting these little guys. Bloody expensive hobby though.