I'm thinking of painting mine in Brunswick Green which many UK engines of this type were painted. I'm slightly concerned about reassembling the timing gears afterwards - I can't quite see how the brass piece down by the cam follower is attached. It might be slid into a dovetailed slot. I'd have to strip it down to be sure. I suppose with careful photographing of the original cam position at exactly Top Dead Centre, it might not be too complex.
They do look more authentic when painted nicely. I saw one on Youtube a while back. This one is a beauty and notice that he has also drilled the main bearing caps for oiling purposes. There are a stack of changes in this one.
https://www.youtube.com/watch?v=dk5p8HCtVUA&ab_channel=TimothyPeace