Following all the great advice given to me I had another go at this colour conversion to black and white.
Briefly: Duplicated layer, added black and white curves overlay. Flattened layers and went to Image - mode and converted to grayscale to decrease file size. Then LCE with unsharp mask settings of 50%, 100 pixels and 0 threshold as suggested by Dave. And the second post is the outcome.
Thanks for viewing. Opinions/ comments/ critiques would be greatly appreciated.