I seem to
recall that the 11/20 PSU doesn't provide some voltage needed by
the RK11-D, and that you have to rig something up to provide it yourself.
The power distribution in 11/20's is though paddle cards that plug into the
slots, instead of using AMP connectors underneath, so it will take some
harness mods to use an RK11-D in it.
Did they ever make a version of the RK11-D backplane which used the paddle
power? They made both paddle power and AMP connector versions of the DD11
four slot backplanes...
--tom