Are they any fictional sources other than the three 2000AD novels that are currently available in print?
Well, "The Keep" was a novel before it was a movie, so you can try to track that down.
There's also the series about the Roman soldier who struck/finished off the Christ (often referred to as Longinus), I think called "Caska" of which at least one is set in WW2.
Comic wise, I strongly recommend "The Light Brigade", it's just about perfect. Nazi's, fallen angels, Longinus, etc...