The exhaust staining doesn't look too bad Kevin. I presume you mean that 'blotch' further to the rear? I had to look close to spot it, so it'll pass.
It might be the lighting, but the wing upper surfaces appear to be in 74/75 , which I thought were still 71/02, but I might have missed something along the way !
Whatever colour, it looks bl**dy good !
EDIT: Missed the last pic. Although near the end of the Battle, drop tanks were available, they weren't used, so for a BoB period machine, you'd need to remove it.
It's one of the puzzles which a number of Luftwaffe pilots have commented about in the past - if they'd had the drop tanks earlier, it would have made a big difference to their effectiveness, instead of making them practice with concrete bombs before undertaking 'hit and run' bombing missions.