At risk of being repetitive (yes, I am
),- First test the direct projection approach: even if you don't have the connecting rings you can do it.
-- Set up the stereomicroscope to low magnification (better not the lower one)
-- focus a high contrast flat object like a printed paper
-- illuminate it with high enough intensity
-- set the 38mm phototube for photo
-- damp the room light
-- remove the camera lens and hold it over the phototube with live view activated, centre it and move it vertically up and down to have an image in focus.
-- taking pictures with high ISO or video could facilitate further revisions
(this is basically what I've done both with the Nikon SMZ1000 and with my Nikon AZ100 microscope to find (approximately) the primary image plane before deciding the adapters needed, not original but a pretty standard procedure)
- The ebay linked eyepiece almost for sure is the normal (low end in Wild line-up) visual eyepiece like mine and very likely like yours. Test yours with a 30mm camera lens focused to infinite* before buying. You can test it with the 30mm tube
* afocal setup, this combo will provide approximately 10 x 30 / 250= 1.2X , the typical recommendation for 4/3 sensors
