I thought this approach might be worth exploring. CactusDave had some spare lenses and an old microscope stand and I had a spare trinocular head, so here are the first results:
This is the experimental macroscope which matches a Zeiss trinocular head with a reversed Pentacon 50 mm, extension ring and DOI HQ teleconverter (the latter to reduce the magnification).
To enable me to use the unmarked focus control, I stuck on a degree scale and used a miniature video camera and TV thus giving a scale suitable for measuring steps for stacking.
Finally, here is a test image of an old hoverfly sample. Lighting was from a microscope lamp and used an old weighing boat as diffuser. You can see this in the first and second photos above. I have also fitted an LED ringlight on the end of the lens assembly, but this was not used in these tests, as although it is great for manual observation, it is not so good for photos (needs a diffuser).
Here it is in action:
