The finder looks like it was modified. Originally they used a 0.965" 30mm or so eyepiece, so the 27mm Kellner binocular eyepiece should work great.
While I hope to eventually fully enjoy the views of my sandcast C8, and the tracking capabilities of its mount, at this point I am quite convinced that the ergonomics of viewing with this telescope do not mix too well with me. One of my difficulties is that due to its short and stubby shape I seem unable to point it close to where I want, and the nice-looking original Celestron 8x50 (? I do not have it here with me to verify the model) right angle finder with a 12.5 mm reticle eyepiece provides a field of view that seems to me too narrow compared to the typical 6x30 finders I normally use. Therefore I get frustrated at the amount of efforts it takes to center the telescope towards what I wish to see.
Among the many accessories I bought with this C8, I found a home-made (or small garage shop-made) conversion to illuminated reticle of a binocular eyepiece. A hole was drilled by the edge of the etched reticle glass, a light bulb and wiring rig was held in this hole by a brass-plated steel ring, and a 1.25" metal adapter was threaded to the eyepiece barrel. Has anyone seen similar conversions?
Comparing the view of this eyepiece with regular astronomy EPs, I would estimate a focal length of about 25-28mm. I have now converted it to a LED light (green diode salvaged from an old router), using for now just some hot glue to hold the light rig in place. If as I hope this binocular EP will make it easier to find the celestial objects I want, I may switch to a more permanent arrangement.