I need to gather some extra info, if you have a second can you measure the stepper shaft you have if you did not buy them from me. The ones I sell are about 22mm I think the shortest is about 15mm if you have one shorter than 15mm could you post the length up here, a pic gets you bonus point. I have an idea but It is going to be a tight fit.
Update- All the sketched ideas are working out really really good. I haven’t decided on a max router size yet, but I don’t think I need to anymore, Should be able to easily make it any cutting width (length literally as long as you want) and any router/spindle/tool width. Getting antsy I need to start making parts to see if the geometry is as rigid as I hope.