I also stumbled across images for a graphic novel called Ascent (2007) by Jed Mercurio which will also deliver some inspiration.
From here I looked into 1940's WWII art work and found these images. They also have a comic book feel with an interesting colour palette.
I used a combination of these images to draw inspiration and produce some concept work. I definitely feel like I am building a visual style towards my final piece. My digital painting skills aren't prolific and I'm quite concerned at how long it takes me to produce one image, so I am going to move on to maya as soon as possible.
Grandad concept 01
Grandad concept 02