I like using the Leica RF lenses with the L->F adapter for close-up work.
"Way Back When", Spiratone (?) made an attachment for copying 8mm and 16mm frames for SLR's. It was a T-Mount device, similar to a slide copier but with more magnification. Might check used camera shops or Ebay. I'll try to find a brand name in the old Modern/Pop Photo mags. We're talking mid 70s.