Oh! Where are his Legs gone? and what's up with his face?
The Maincolour is a little too dark imo and you shoult try to take a little more care of the metal parts, with corrosion, scabby blood and other nurglish things and get rid of the Grades on the Legs and try to drill the Bolter-Barrel!!!
it took me some time to realise he was standing i water. you could go with a bit more color or stuff too help make that clear.
otherwise: i find your conversion-idea pretty sick! which is cool for death guard!!! even though it's not my kind of color-sheme i find it real cool!