I solved the clearance problem of using a 50mm lens on the turret w/o using spacer. I just picked up a Fujinon-EP 50mm/f3.5 lens (at a good price). It does not stick out back as far as the EL-Nikkor. I mounted it with the flush adapter w/o a spacer and the turret rotates just fine. So if the EL-Nikkor does not focus with the spacer, I have a backup plan.

Just that on the Fuji, the aperture ring turns in the opposite direction from the EL-Nikkor. Oh well, that's what I get for not using a matched set of lenses on the turret.

Now I am wondering if the Rodagon or Componon-S are similar to the Fuji, and don't stick out back as far as the EL-Nikkor.