Photos of the illuminator 60 below. The bulb and its holder fit into a hole slightly bigger than 2 inches – I tried a 2 inch astronomy eyepiece in it and it was slightly sloppy – I suspect a 2 inch bulb holder or 1.25 inch holder in 2 inch to 1.25 inch astronomy eyepiece adapter could work as an alternative to the existing bulb holder if tape was used to slightly enlarge it.
Please note this same illuminator is on both my Zeiss IM and Zeiss IM35 microscopes.
Andy