lyle,
that's great talent

With these types of images Colors>Curves tool is your friend.

Color mode layer + Curves + Patience, as said before. I would probably play with Color Balance too, in order to unify hues. Besides, I'd say you need two images with more or less same lightsources, else you'll spend some time learning how to define shapes, volumetrics, depth on a flat screen

Very good point about the light sources.

My wife goes crazy over animal morphs and saves everyone she can find. She keeps wanting me to start making them.

These would take some practice/time
black squirrel in the yard and a black panther