[Geoff45 (Geoff)]

OK Lee, here we go:
I didn't use your luminance because I didn't know how you'd done it. I generated a new synthetic L from your R, G and B and used that instead.
--Load R, G and B images. Do a LinearFit with G as the reference.
--ChannelCombination
--CloneStamp to remove stray red, green and blue pixels.
--DBE
--BackgroundNeutralization
--ColorCalibration with M83 as the white reference
--RGBWorkingSpace with colour coefficients set to 1 and gamma set to one. The reason for doing this is to extract a linear luminance image in which R, G and B all contribute equally.
-- Image > Extract > Lightness (CIE L*). I used this as my synthetic Luminance. Stretch with HT
--Clone and clip synthetic L for use as a mask for the RGB image

--Back to RGB image.
--Stretch with HT
--Boost saturation with Curves, using the clipped synthetic L to mask the background.
--Noise reduction with ACDNR, using the clipped synthetic L to mask the bright areas. Go strong on the chrominance noise.
--SCNR to remove green cast.

--LRGBCombination
--Masked saturation boost with Curves
--SCNR
--Convert to sRGB for web display.

The image would probably benefit from a deconvolution as well as a light noise reduction on the final image.
Geoff