By sheer luck it turns out that the DR400 and KX250 steering stems have exactly the same bearings, so it will make the fork swap a lot easier. The DR stem is on the left. If anyone wants to do a fork swap then I came across this useful document located at:
http://www.ohiocaferacers.com/OCRStemSizes.pdf
http://www.ohiocaferacers.com/OCRStemSizes.pdf