I'm sure that this topic will generate quite a number of postings!
Keep in mind that aircraft can have different schemes at different times. So your DH4 probably had the horizontal stab painted PC10 for most of its life, but it may have had it painted red for a short period. Same for the rad cowl: bare metal early in its life (when the photo was taken), but red later on for whatever reason.
Various interpreters will interpret variously. What colour was the cowling of Voss' triplane? What colour was the upper surface of the upper wing of Lothar von Richthofen's triplane? In a fair number of these topics, no firm evidence one way or another has been found to date. So you can just about pick the scheme that you think is right, for your reasons, and do the build. As long as you do your research thoroughly, and can justify your decision, you will be on pretty firm ground.
You spoke true when you said, "you want build it as close as possible to the real airplane." Note: "as close as possible." Sometimes there will be no question as to the scheme to use, while at other times you will have some leeway due to incomplete or diverging interpretations of the scheme. In these cases, it's your call to make based on what you've found out in your research.
Based on your post, you have four options: red cowl and either red or PC10 stabs; or bare metal cowl and either red or PC10 stabs. Crossreference your sources, trying to see if one or more of these combinations works or, if not, if one or more of them are more likely than others. Weed out the ones that don't add up, and you will be left with those that do, or almost do. Then it's up to you to make the call and start the build! It sounds to me like the cowl was red (all of the information you have says so, less the photo), with the horizontal stab in PC10 (most of the information you have says so). If you're happy with this, then you build. If you want to confirm one or other point from other sources, continue the hunt.
Hope all this blather helps. Good Luck!