Actually Wayne here has a point - I don't remember seeing any 400-series on my Lists of JG 301 D-9's (mostly 21xxxx and 500xxx, if memory serves - I am not at home or near my list spreadsheets).
There are pro's and cons to this of course - a 'cowl demarcation' does not a confirmed manufacturer reveal (as power eggs were dropped and swapped all the time - esp on the later a/c); for this we really need to see the main body of the fuselage. Wings were often swapped, tail units replaced, power eggs changed, etc. The next con is that the 500-series is where Japo and EE diverge the most; Japo suggests the 'cream' RLM76 (or 'Light RLM02') colour, with a mostly RLM81 fuselage pattern (with RLM81/76, RLM81/82 or RLM81/83 wings, depending on a/c), where as EE suggests a much 'greener' appearance.
The pro's are the available references show almost thing you want them to show - OK, you're probably stretching things a little if you want to suggest one of the 600-series RLM74/75/76 D-9's (ie, white fuselage Balkenkreuz), but beyond that, there is very little that you could do within the known D-9 limits, that would not be considered reasonable...
I will double check what I have on hand once I am home - net there is busted ATM; hopefully will be fixed by the time I get home.
D