The 26 mounting ring is identical to the 24 ring, except for the lettering. I use both on the Zeiss MP 100, and have also put on the Canon 180 macro. You can also mount the heads on separate goose neck holders that you can attach to the tripod socket of the body. Haven't used mine on a 35 mm (have a Zeiss 35/1.4 classic), not sure it would illuminate properly. I would rather use my 580 with diffusor and reflector.
For the Zeiss 100 and the Canon 180M, there are Canon adapter rings, so no additional step ring required. I leave the adapter ring permanently on my Zeiss 100. Hood goes over it no problems, and ring does not vignette even at infinity focus.